Let's start with Rowena.
Rowena's the one conscripted to find a way to cure the Mark of Cain. She has been chained by Sam, forced to go over every page of the Book of Damned to find the spell that will finally save Dean. Her drive is simple: find the cure to remove Dean Winchester as a threat to her via the Mark of Cain and First Blade and gain her freedom in the process. It is her reason to help---for if she doesn't, the alternative isn't a pretty one.
Rowena represents the most simplistic version of balance or lack of balance within the show. She gives voice to the rules of magical balance in “Dark Dynasty” when she answers Charlie's question. Rowena knows that to create or break a curse, one must accept that another curse must be created in return. Magic and its wonders come with a price---and while something may be affected by it, in many ways that thing isn't actually destroyed but merely transformed or replaced by something else. She, as a Grand Coven trained witch, understands this fundamental of her craft. She knows that to do this spell is to invite a reaction. She also knows that the spell itself may cost her something significant.
At the beginning of “Brother's Keeper,” Rowena is facing a serious imbalance. She is in chains, forced to work for the Winchesters---or at least “Samuel.” Rowena may have labeled Crowley “their bitch” at one point, but now that she's locked into doing their bidding, she's more likely to earn that title. For Rowena, her imbalance comes from her lack of freedom. She's been trying to acquire that for centuries. First from those that chased her from her homeland of Scotland, then the Grand Coven, then Crowley, and now the Winchesters. Rowena wants to have the freedom and power to use her magic when she sees fit as she sees fit without any fear of anyone else threatening her.
When it comes to her fleeing Scotland in the first place, we're left to wonder how much that had to do with witch hunters or her desire to break free from the child she never wanted: Fergus. He held her back, got her ostracized from the Grand Coven, and forced her on the run. In that regard, Rowena saw him as an imbalance to her life---the family that held her down and kept her from reaching her true potential and inner balance. So she ran.
Along the way, she meets a terminally ill young Polish boy named Oskar---and instead of feeling nothing for the boy, she actually loves him deeply. It is this boy that will become her weakness and add to the imbalance she's experiencing in the present. After all, loving him will be precisely what the spell to cure the Mark of Cain needs. So, when she's confronted with Oskar yet again---called into the room by a smug Crowley no less---she snaps at her son, “Even for you, Fergus, this is a new low---a cruel shameful disgusting low.”
This is her moment to decide, however, how she will approach the imbalance question---and the most powerful force within Supernatural: family. While she's expected to make this sacrifice in order to cure Dean, no one is truly making her go through with it. Crowley states, “It's only cruel if you actually go through with it---though, who's the cruel one then.” Technically, Oskar was only alive now due to her magic. She had give him immortality, and one is left to wonder what that cost in the long run for the witch. Now, however, he stands before her confused and afraid. Rowena obviously still cares for this boy---now 300 year old man---as she refers to herself as Auntie Rowena. She saw this boy as special, someone to cherish, and had been driven far enough by that familial emotion to save him from death.
Now, however, Oskar stands in Rowena's way the same way Fergus once did. It's either choosing to keep him alive and remaining chained or sacrificing him and finishing the spell that will grant her freedom. If she goes through with it, she will have held up here end of the bargain---and have leverage over the Winchesters to boot. Rowena pulls the man close and viscously makes her decision when she stabs him in the throat. His blood is forced into the bowl and Rowena promptly chants the spell that will not only restore her balance but cure Dean from the Mark's evil.
Rowena's choice to reject family may have great consequences. The witch may have been doing this spell for the Winchesters---at Sam's orders---but it is her actions and her magic that is in play here. Rowena is doing these things. As she casts the spell, balance may be restored to her---after all she breaks her chains and uses her more potent magic on Castiel and Crowley equally to further her familial rejection----but in return the world's balance may have been disrupted by this. Rowena had to know that whatever the reaction to this spell was it'd be something dire---and in this case it is a release of the Darkness, an ancient evil so frightening that God and the Archangels locked it away via the Mark itself.
In this way, her familial rejection---while helping the Winchesters perhaps save theirs---has global consequences yet to be understood.
If Rowena rejected family in favor of restoring her balance of freedom, how do Crowley and Castiel provide balance for one another and how do they choose family to maintain or restore it?
Crowley and Castiel balance each other naturally. One is a demon and one is an angel and their dual existences in many ways cancel one another out. Over time, Crowley has done a lot of bad but has leaned towards doing a little good---he helped them against Lucifer, he helped them against Abaddon, and he helped them cure Demon Dean. Castiel, on the other hand, has done good things or has been considered good while doing some bad here and there---such as taking the mantle of the new God, releasing the Leviathan, and lying about the angelic civil war he was waging. Over time, both have seemed to balance each other, providing excellent counterweights that make them see one another differently. As they are both supernatural creatures connected to the Winchesters, its no wonder that they've also come to see each other as more than simple adversaries on different sides of the same coin.
Crowley, as angry as he was with Sam in “The Prisoner” answers Castiel's summons. He may be annoyed and wonder “Who summons anymore? couldn't you call?” but he is prepared to hear the angel out. Crowley may have chosen to become more his demonic self and threaten Sam with death, but when it comes down to it, he can't help but choose the Winchesters and their latest cause. On the one hand, it's obvious that Crowley does this out of sheer self preservation. After all, the longer Dean bears the Mark, the more of a threat he becomes to Crowley's throne and life. He can't have the ticking time bomb waiting to go off. On the other, Crowley has shown over the last two seasons that he's grown to care for the ragtag Winchester family---and that includes Castiel.
So, Crowley agrees to acquire the required ingredients that are necessary to complete the spell.
Crowley also chooses to reject family---something that will have dire consequences through Rowena's actions. His choosing to jump on board Team Winchester has a sinister element. He may want to help Sam and Dean on some level, but he also wants to punish Rowena for her rejection of him by striking at what matters most to her heart. So, Crowley rejects her in favor of the Winchesters, bringing to her the one man that may mean something to his mother. In doing so, he delivers a cutting speech that seals his rejection. He does so in order to make her feel as he does. He tells her, “All my long life I wondered what I'd done to deserve a mother who refused to show love. I pined over it. I built my bloody kingdom on top of it. Then one day an epiphany struck. My mother was incapable of loving anything. For the first time, in hundreds of years, I felt free. Then you showed up in my dungeon. We communed. And I began to realize you weren't incapable of love, you were incapable of loving me.”
Castiel, on the other hand, is merely facing his own imbalance by watching the Winchesters being imbalanced. He voices the fears that they may face a greater consequence when the spell to cure Dean is cast, telling Sam, “If she removes the Mark using the Book of the Damned, what are the consequences?” and yet when faced with the absolute terror and imbalance of Sam's desperation, he folds and agrees to champion the brothers once more. There's little he can say or do in the face of Sam's shout, “Dean guessed!” It's why, while Sam is hunting down Dean, Castiel goes to Crowley in the first place. Knowing that he can't simply flit around the world post Metatron's breaking of Heaven, he must rely on the King of Hell. And so, Castiel summons the demon.
When faced with Crowley's disdain and sheer anger---after he shouts at Castiel, “Maybe I'd feel a little different if Sam Winchester hadn't just tried to bloody kill me!”---Castiel remains undaunted. He won't allow this explosive anger to deter him from his new mission. And as he faces the moment where it seems Crowley won't help, he makes a move as if he's going to use his grace to kill Crowley, only to be told, “Blast me or beg.” Castiel probably had no intention of actually killing Crowley anyways---something the demon fully knew all too well considering the desperate situation they face. So, he's forced to acknowledge Crowley as “King” in order to get what he wants from the King of Hell.
From there, it's simply watching and waiting for Rowena to complete the spell. He is fully ready to make good on his promise to Sam that once she has done it he'll kill her and remove her threat from the world---thus his attempt to restore balance for using her in the first place. And yet, as the spell rockets out of the warehouse room they wait in, he's forced to confront a powerful and angry Rowena. She breaks the chains and turns Castiel on Crowley---something that further seals the acceptance of these two as family within the Winchester nexus. Crowley is genuinely concerned about the angel, shouting his name---both fearful for his own life and for what Rowena's managed to do to Castiel after gaining her freedom. In a reversal, Crowley's begging is an attempt to break through to Castiel, to somehow reach through to that strange familial tie that connects them---and to stop what she's done to them both before it is too late.
As Castiel is forced against his will to move against Crowley, we're left with the fear and anxiety that they've been forced to reject one another and create another imbalance---or if they're able to find a way out of the situation and stand yet again as opposing yet equal forces for Sam and Dean against the next great evils in both Rowena and this mysterious and powerful Darkness.
If Rowena's rejection of family restored her balance, if Castiel and Crowley provide their own balance by accepting one another---then it is Sam and Dean that are the ultimate example of balance and family power within Supernatural itself. They are the essential pair, the ones that all of the familial power revolves around and when that balance is upset wreaks the greatest havoc on the grandest of scales.
At the start of “Brother's Keeper,” Dean is severely imbalanced by what he's done with the Mark. Being imprisoned within by the end of “The Prisoner,” the real Dean has been largely submerged under a darker and ruder version. He is still committed to hunting down monsters, killing as many of them as he can as he goes, and yet he lacks all of the finesse and sympathy required to do the job well and correctly. It's evident the moment we see the balled up fist to the rude comment about the victim. He tells the local police, “Who let her leave the house looking like a whore.” While Dean may certainly have thought that under normal circumstances, he would have never voiced it to this cop in such a callous manner if not for the Mark's imbalance twisting him further.
It only becomes worse as he goes to the home of one of the missing girls, demanding to know what happened to their daughter. There's no sympathy, there's no attempt to console or be sensitive even if that's required to get the job done. For Dean here, this is an inconvenience. He's faced with having to do this to get to what he really wants to do: killing the vampires responsible. This is holding him back, a hindrance to what the Mark wants him to really do. It doesn't care about why Dean does what he does or what he'd normally try to do in “saving people, hunting things, family business.” It simply wants him to kill. Now.
So, Dean goads the father, telling him, “Then I came here and I smelled the deceit and the beatings and the shame that pervade this home and you know what I don't blame Rose anymore. No wonder she put on that skank outfit and went out there looking for validation---right into the arms of the monster that killed her. Joe, who did this?” It earns him a few strikes to the face and he pulls a gun, almost as if he is willing to kill this man just to kill. When he gets the information he wants from the son hiding in the hallway, he makes his way to the cabin and doesn't bother to talk down the frightened and skittish vampire holding his fellow hunter, Rudy, hostage. He doesn't bother to make sure Rudy walks away from this hunt safely. Instead, he goads this man, too, showing just how imbalanced he's become---going so far as to make a loud sound to cause the knife to plunge into Rudy's heart and leave him dead.
Much like working the case had been, Dean found Rudy an inconvenience. He was here to kill these vampires, Rudy was in the way of that, so he did what the Mark wanted in getting right to it. Once Rudy's out of the picture, Dean has no hesitation in decapitating the vampire and loosing one of the female victims---traumatized now more by Dean than by the vampires. He's non plussed by her squalling, telling her, “I just rescued you, you're welcome.”
It isn't until the hotel bathroom that Dean realizes just how imbalanced he's become and how bad it really is. His imbalance is created by the Mark of Cain, yes, but in turn it is also created by the sheer rejection of both Castiel and Sam---his family. He brutally beat Castiel and fled the Bunker, telling him that they should both stay far away from him. That action combined with Rudy's death haunt him. One of the only reasons Dean had held it together up until now is because he was able to rely on the family he has in Castiel and Sam---that they'd watch him and pull him back from edges. Now, however, not only has he pushed them away due to his anger but he is a danger to both given by the guilty images he sees of Castiel's bruised face. Next time, he may not stop. Next time, it could be Sam.
Dean, driven to anger by these images, guilt torn and frustrated by his obvious loss to the Mark, smashes the room to utter pieces. He breaks the mirror, he tears out and smashes the television, he throws furniture---all in a physical display of his defeat. Dean has no more moves left. He's lost to the terminal disease that is the Mark, and its imbalance is now hindering his ability to do his job---the one he swore he'd do until he couldn't do it anymore. That time has come, and so he leaves a note for Sam, knowing that his brother will track him down eventually anyways.
Desperate, Dean summons the one entity he's certain can do what no one else can: Death. Only Death can kill him, only Death can stop his monstrosity and imbalance from further harming those he loves or the world around him. He can't help but remember Cain's words, too, that the kill list he will eventually commit hangs out there: Crowley, Castiel, Sam. To prevent that, he will have to have Death remove him from the board.
And yet, due to the nature of the Mark's absolute imbalance, Dean can't simply be killed to restore it. It takes more than that---a lot more that will leave Dean with another difficult decision.
As he finally answers Sam's desperate call, he tells him, “Brother, I'm done.”
Death is waiting, and Dean isn't going to say no this time. It's too late to save him, and he knows it.
Sam makes his way to the bar, and there Dean tells him the awful truth Death has told him. Dean can't die. The Mark isn't simply some evil trick Lucifer played on Cain. It's not something he merely gave to Cain to corrupt God's prized creation in humanity. This evil was what had twisted Lucifer himself into the corrupt angel he's known as now. Death tells Dean, “Before there was light, before there was God and the archangels there wasn't nothing, there was the Darkness. A horribly destructive amoral force that was beaten back by God and his archangels in a terrible war. God locked the Darkness away where it could do no harm, and he created a Mark that would serve as both lock and key, which he entrusted to his most valued lieutenant -- Lucifer. But the Mark began to assert its own will, revealed itself as a curse and began to corrupt. Lucifer became jealous of man, God banished Lucifer to Hell, Lucifer passed the Mark to Cain, who passed the Mark to you -- the proverbial finger in the dyke. ” The Mark is a lock and key---a prison for this dark and encompassing evil that they can never let out.
Dean can't be cured or allowed to die lest it get out---unless he's willing to pass the curse onto someone else that will endure its burden. Dean refuses, leaving Death to provide balance another way. As the ultimate agent of the Natural Order, Death has to make sure there's no way to undo what he is about to do. He needs Dean to remain with the Mark and he knows that he can't necessarily leave Dean on the board to keep that intact. Yet, if he actually sends Dean to “some place not on this earth” he is left with Sam preparing to upset the balance he's so carefully created. So, the only way to make this work is for Sam to die and for Dean to agree to go to this created space to keep him and others safe from the Mark's evil.
Dean, pushed so far by his imbalance upon rejecting his family at the end of “The Prisoner” actually agrees with this plan. He tries to convince Sam that it's the right thing to do, telling him, “You were right, Sam. You knew that this world would be better without us in it---why cause we track evil and kill it? The “family business,” is that it? Look at the tape, Sam. Evil tracks us and it nukes everything in our vicinity. Our family, our friends. It's time we put a proper name to what we really are and we deal with it. ” Dean is reeling from the injury and evil he's brought in this last case he worked---and by what he did to Castiel---that he sees his family and his existence as a dangerous imbalance itself.
And yet, as the brothers fight both physically and verbally, Dean has to confront his imbalance head on and make a decision. Either he goes through with this and allows Death to remove him, or he chooses Sam and their family and accepts what happens next. Dean has bested Sam in their combat, knocking Sam easily aside and to his knees to take a defensive stance. As he looms over his brother, Death gives him the Scythe, and Dean prepares to execute Sam.
The longer he stands over his brother, staring down into Sam's eyes, the longer it takes for Dean to make the move. He pleads with Sam, “Close your eyes, Sammy.”
The more he hesitates, the more his decision no longer seems cut and dried. To go with Death's plan may keep the world safe from this Darkness---but in return Dean must commit an evil atrocity to get there. Every fiber of Dean's being is to save Sam at all costs, that his brother is precious, and that he will never be like Cain. The longer Dean stares down at Sam, the more he realizes not only will he be killing his brother as Cain said his story would end, he'd be punishing Sam for his own sins. He knows he'd spend an eternity with the knowledge that he ended his brother's life---a proposition that is a thousand times worse than any experience he ever endured in Hell. To kill Sam is to commit another evil act---and how can committing an evil act lead to anything else besides more evil?
As Sam lays down the family photos, Dean is left to stare at them. His brother's words wash over him, and he can see that family is truly the balance he must choose over this plan with Death. To do this is to further his imbalance---to stop and choose Sam is to restore it. It is clear cut---but when Death delivers the line, “It's the family you must proceed, Dean. To be what you are, to become what you've become is a stain on their memory. Do it, or I will.” that tips the scales.
Dean, knowing Death is wrong about his family and this choice, makes a last ditch effort swing. He knows that the likelihood they'll go down here at Death's hands is almost certain, but Dean will take it rather than kill Sam himself. He swings the great blade over Sam's head and rounds until it stabs straight into Death. The gamble Dean makes in choosing to save Sam and accept his family works. Death crumbles before them, defeated.
Moments later, the spell Rowena has cast strikes, and Dean is not only finding himself balanced by choosing Sam over the imbalance of the Mark or Death's proposal, he's also finding himself whole once more, no longer facing the agony of the Mark.
If Dean choosing family in the end managed to re-balance him, how about Sam? How does he find a way to achieve balance and how does he use family to do it?
Sam is imbalanced by his desperation to save Dean. He is so driven to do whatever it takes, driven to the brink by what the implications of failure might mean for him. It is the very imbalance that he cannot tolerate for much longer. Either he restores the balance that he and Dean share, or he dies trying. It cannot be any other way. He refuses to leave his brother with the Mark. Castiel, confronting him about the consequences that may arise, only makes Sam's desperation tick up further. He shouts at the angel, “And then what? The only thing that stopped Cain was death, do you wanna kill Dean because I don't. And the only way I know how to save my brother is to cure the Mark, and yes I know there will be consequences; but not you, and not Dean, not anyone can tell what those consequences are. So I'm not going to let my brother d-destroy himself on a guess... We save Dean.”
Focused on getting the spell together, he's flabbergasted when he learns that it consists of the forbidden fruit, the golden calf, and the heart or love of Rowena. It matters not, they'll find a way to get what they need and he will save Dean if its the last thing he does. Finding out from Rudy just how far off the rails Dean has gone, Sam must leave the operation in Castiel's hands. He has to find a way to stop Dean, to save him from himself, and to buy some time for them to make this spell work. It's the only thing he can think to do, and so he follows his brother's trail.
His first stop is disturbing and shocking. Dean has left a mess behind him after he killed the vampires---and as Sam walks into the scene to assess, he's confronted with Rudy's body. The sheer knowledge that his brother managed to get Rudy killed on this hunt ticks his desperation up all the higher. Sam knows now that time is running out faster than ever---and the devastated expression that settles over his features reveals just how saddened he is by how far gone Dean really is.
But it's not the worst thing he'll find.
Upon finding Dean's trashed room, Sam is crushed by just how broken Dean has become. He sees all the carnage, the explosiveness of the rage inside his brother, and knows that he has to find Dean quickly. It isn't until he sees the note on the bed that Sam realizes just how little time they have left. It doesn't escape Sam perhaps that this is the second note that he's found like this. The last time, Dean had written it as a demon, begging him to let him go. This time, it's more cry for help, a last act of a desperate man. The Impala's keys are left with it, and Sam knows now that Dean has left to die---or find some other way to stop himself. He has little time to waste if he is going to succeed in saving his brother now.
As Sam rushes up to the bar, however, he finds something he didn't expect. Sam had expected to see Dean wallowing, angry and afraid. He perhaps expected Dean to be drinking himself into a stupor. He may have expected Dean to be toying with various methods to kill himself or to at least try. Sam may have even expected the black eyed creature he hunted down earlier. Instead, he is stunned to find not only his brother there, but Death waiting.
As they bombard him with the plan to stop the Darkness, that Dean can't stay on Earth, Sam is incredulous. He shouts, “What, he's going to---going to send you into outer space! This is madness, Dean!” This is a curve ball Sam never ever expected to walk into---and now he has to think fast if they're going to get out of this one with time spared for Rowena to get what she needs.
Dean had already dropped another bomb, telling him, “Truth is when I left, I thought the only way out was my death. Well, I was wrong Sam, it's yours.”
Sam, knowing he's facing not only a threat to his brother but now to himself, can't simply let that happen. Not only does Sam not wish to die, he also knows just what type of punishment this would be for Dean in the end. It would forever destroy the balance they are forever trying to maintain or rebuild again and again. It would destroy the familial bonds they share and render it powerless if Sam stands by and allows this to happen.
Dean labels them as evil, reveals that he sees their lives and what they do as deadly to those around them. They pollute the world, they get people killed, and they don't help as far as Dean is concerned. Sam, unwilling to submit to this dark logic, retorts, “We are not evil. Listen, we're far from perfect, but we are good. That thing on your arm is evil, but not you, not me.”
Dean further pleads his case---pointing fingers squarely at both of them---labeling them as evil. He points out that he let Rudy die. He reminds Sam of how he convinced Lester to sell his soul---and how he “bullied” Charlie. As far as Dean's concerned, none of these things led to a “good end” or a “just end.” To go with Death and to kill Sam is to remove them from the world---and to make it a better place without their “evil” in it. Again, Sam tries to break through to his brother, to pull him back towards their balanced axis. He replies, “You were also willing to summon Death to make sure you could never do anymore harm. You summoned me because you knew I'd do anything to protect you. That's not evil, Dean. That's not an evil man. That's a good man, crying to be heard, searching for some other way.”
Desperate and imbalanced by Dean's imbalance---and unable to make Dean hear his words---Sam makes his move fast. It's a rough jab to Dean's face, initiating a fight. Often it's Dean that starts these fist fights, but Sam knows he has to try and wake Dean up somehow. Physically taking him on is a losing proposition. The Mark gives Dean more strength and wallop than Sam has right now, but that doesn't mean he won't take the blows and deliver some of his own. In many ways, it's a calculated risk to maneuver Dean into seeing what he wants---to make his case and prove that family is the only way they can balance things---no matter what case Death tries to make in kind.
Sam is forced down to the floor, curling in on himself after several painful punches to the face. He covers his head and pleads, “Enough, it's enough.” The action itself is designed to give Dean pause, to move into the next phase of his case. He can't beat Dean, and he can't get through to him that way, then he'll have to do the next thing he knows might buy time.
Staring up at his brother, unwavering, he tells Dean, “You'll never, ever hear me say that you--the real you is anything but good. But you're right, before you hurt anyone else, you have to be stopped at any cost. I understand. Do it.”
It is this seeming submission that will really strike a chord with Dean---and Sam knows it. When Dean tells him to close his eyes, Sam remains steadfast. He keeps his eyes trained on his brother, not willing to break the possible last contact he might have with him.
And then he plays the last card he has in his deck.
He pleads softly, “Wait. Take these. And one day, when you find your way back, let these be your guide. They can help you remember what it was to be good. What it was to love.” He lays down the photos that had helped him get through his search for Dean and the cure that they had to both endure, and forces Dean to look at them before he makes his next move. They're pictures of their mother, of Dean and his mother, of family. It is their family, the reason they've continued in this life long past the revenge trip John started against Azazel. This is the family that they've carried with them throughout each fight---and it is the family that has given them the balance they need to stay together as a pair, keeping each other grounded, pulling each other back when necessary---even if that means a drastic over-correction sometimes.
If Sam must face this execution, if he must die for the greater good, then he will remind Dean that he, too, is good and that they are good. If he must face this moment, he won't let Dean do it alone. And, much like the last ditch efforts he's watched his brother make throughout the years, Sam is making one last ditch effort to go down swinging. At this moment it may not be with his fists or weapons---instead he'll do it with his heart.
Once he's finished, Sam finally closes his eyes and feels the blade whoosh over his head---only to have it spear Death himself.
As they watch in awe as Death crumbles, a huge lightening strike hits his brother and the Mark is finally removed. Sam had managed to buy time---although he didn't realize they were this close to acquiring the ingredients---and now that he manged to not only get through to Dean with his case, he's also managed to finally save his brother as he said he would from the Mark.
Just as the brothers are balanced once more, however, Death's ominous prediction comes true. Red lightning and dark black smoke clouds larger than any demons they've ever seen shoot from the ground and rush to make a giant cloud. They're left with little time to flee, with little time to appreciate their balancing.
In many ways, the balancing that takes place after the spell Rowena casts is an internal struggle inside Dean via the Mark becoming external in this Darkness.
Now that the brothers have managed to balance one another once more, perhaps they can now face it together as the unit they are---for it will be their familial bond that has the only real chance of standing against it and restoring the balance to the world in its evil wake.
In the end, they'll have to be each other's “Brother's Keeper”---as it always should be.