Amazing grace, how sweet the sound,
That saved a wretch like me.

Sacrifice. The operative word on Planet Winchester. Almost ever since we became acquainted with Sam and Dean, and their real and surrogate family, we also witnessed, broken heartedly, how they were ready to give everything, literally everything, to save one another.
Mary sold her soul as a young woman to save John, and I doubt she realized the extent of her deal that moment. John struck a deal to save Dean’s life. Dean sold his soul to bring Sam back. Bobby pawned his to help the men he loved like sons. Sam endangered his soul by drinking demon blood to stop the apocalypse and eventually allowed Lucifer to ride his body in order to save the world.

I have grown accustomed to the various emotions still haunting me when thinking of Sam’s last decision, but my heart still breaks for him.

Although I have loved Dean for his bravado and sharp tongue and all the good traits that are his amazing nature, I have always carried Sam in my heart – if you can say that about a fictional character. Some of his reactions seemed familiar to me and I loved his gentle soul and, frankly, I somewhat fell in love with the guy. He will always, always be in my heart with the other great characters I’ve grown to love ever since I started reading books or watching movies and tv. So will Dean, but not as intensely as his younger brother, I have to admit. I have to thank Kripke and all the writers for that – for giving me, us, such complex, beautiful, multi-layered fictional characters.
With the deep affection I’ve felt from the beginning for Sam, I have followed his journey with great curiosity and, as dangerous clouds darkened his horizon, with trepidation and concern.
He evolved to a really grown up person, distanced from the young rebellious guy who could throw a tantrum over one of his father’s words. Well, he was forced to grow or else he might have lost his sanity. In the beginning he still wanted to return to a ‘normal’ life, the kind he had planned, in vain, with Jessica, leaving the family again after they would have found dad.
That, however, changed. Eventually he sought peace with revenge, not being able to bear the pain of losing his brother to hell otherwise… the guilt over that must have consumed him – after all, Dean died at the claws of hell hounds for Sam’s sake, having sold his soul because he could not live without his brother.
Easily he fell for Ruby’s bait and trusted her, at some point perhaps loved her, because she became the only stable factor in his life after Dean was gone, and he pushed others, like Bobby, away. Sam dealt with grief in an aggressive way – on the one hand seeking revenge, on the other punishing himself, thereby turning the aggressive energy inward which must have felt like a red hot iron slicing into his soul.
He had to survive one of the most difficult journeys a human being can – realizing that his good intentions had in fact brought about a disaster and not being able to find redemption, yet. On the contrary – he suffered his brother’s mistrust and anger and guilt which Dean directed at him, in the beginning of season five without any mercy.
Sam had no other intention but to do the right thing. He did what he believed to be right. That this eventually helped Lucifer out of his cage (just as Dean’s breaking of the first seal, equally unbeknownst to him) was not the intended goal. His only mistake probably was to trust the wrong person, sorry, demon, and believing in his powers. He was also hoping to find peace with revenge, I think.
Well, we know what happened.
Sam spend almost the entire fifth season trying to redeem himself. He fought desperately to win his brother’s trust again and often he didn’t know how to do it, because what ever he tried Dean had trouble letting him back in. The atmosphere in the brothers’ relationship was tense, soften sometimes with humour and/or danger, but it took Dean almost all twenty two episodes to see Sam at eye level and trust him again, unconditionally at a high price, though.
Sam must have suffered like a dog, but he managed to get through by functioning and doing his job. Not the worst strategy, even though the pain about the situation and his desperate wish to take it back must have eaten away at him like one of those hellhounds. 
He found something else to help him through: hope. A most amazing development, given the difficulty of their situation.
He remembered their job ‘saving people, hunting things’ and their responsibility to save the world from the angels having their little ‘pissing contest’. He dragged Dean who had almost given up back into the game and was hugely accountable for Dean changing his mind and not saying yes – because his elder brother didn’t want to let Sam down. A sign that Dean found his way back to his brother again, even before he voiced it.
In the end, finally, he saw a chance to set things right – as he said in the first episode, he’d ‘do anything, anything to take it back’ – and took it.
Bloody stupid plan that was, Sam. And how amazingly brilliant, too.
The moment Sam mentioned the idea to Bobby on the phone we knew he was going to do it. And we also knew that he would not do it behind Dean’s back. Not betray his brother’s trust again.
The situation was desperate. Forlorn and hopeless. Their chances at beating the devil were low, but it was the only thing to do to at least try to save billions of people.
So, Sam let Lucifer in.

I can’t even begin to imagine how it must have felt to be imprisoned in your own body that was controlled by the greatest adversary possible. Lucifer pushed the right buttons to drive Sam insane in there – he made it clear that he had influenced his life from the very beginning, making sure, his path would lead him exactly to this very moment – putting his prom date there, his teacher, some friends… Azazel’s gang.
He had been hovering on the brink for a while, but his was more than Sam could bear. His face in the mirror after Lucifer blew off â€˜some steam’ speak volumes – this kind of destructive anger might have been Sam’s modus operandi in an earlier season, seeking revenge on Lilith, but it was not now. The only anger he felt was directed at Lucifer who needed to be destroyed.
With what he learned from Lucifer the final pieces of the puzzle that was the enigma of his life and his feeling different fell into place. The sensation he had known all his life was confirmed again, but this time Sam was ready to deal with it.
Coming to the decision to let Lucifer in was one of the most thought-through resolutions of his young life, and this time with his brother’s consent. He would not allow Lucifer to affect him in the way he had done in the past with all those manipulations.
It needed something else, though, to find enough strength to overcome the lightbearer. Sam spent many of his last moments in anger, I assume – entrapped in his own body, fighting desperately against the dark fiend, trying to find the necessary force to conquer him. Knowing Sam, as Lucifer killed Castiel and Bobby, and almost beat Dean to death, he probably raged more in there than he had ever in his life. But it didn’t help him.
Lucifer stayed in control.
That is, until countless memories reached Sam’s soul with the light caught in the metal of the Impala. From the army man in the ashtray to the tight hug the brothers shared after Dean had brought Sam back. Memories that were nothing else but expressions of closeness and love and kindness and attention, of respect and of fights, in short: of a deep bond that was never destroyed no matter how strongly the dark powers tried to achieve that.
It may be that Sam was very angry during his last hours, but in the end, when it really counted – love was the driving force that helped Sam take back the reigns and jump into the black hole.
He gave everything he had to give – his life. He did it out of love and the wish to set things right. His deeds in season four had hurt his self-esteem badly, he felt to be the least of all his family and friends, and still he became the most important asset there was to put Lucifer back into his cage.
We don’t know yet how Sam came back or what grace raised him from the pit. I would like to believe that his great sacrifice secured what he yearned for the most: redemption. Forgiveness. Being worthy of his brother’s love and trust.
I understand why Sam was so desperate for that, but I never saw him with the unforgiving eyes Dean looked at him in the beginning or the malicious eyes the angels followed him with. I was hoping for him to finally see what a decent and brave human being he is, and I hope he will find the strength of his soul again, as he did when he brought down Lucifer.
As the essence of this show has always circled around the many faces of love and family, it was only logical and pure that in the end love was the power that helped them. ‘We’re still working on the power of love’ Dean mocked the others in an earlier episode, but in fact that was exactly the power they needed. Hopefully, it will help Dean come to terms with losing his brother – and Sam finding his way back into life after – in all likelihood – horrific experiences in hell, even if it was ‘only’ the hell of feeling Lucifer’s presence in his body…
So, at this very point, in the soft mood of this article, and still moved to tears by Sam’s ordeal, I will interpret his eyes at the end of Swan Song to hold an expression of love and relief, that Dean is not alone, that he did the right thing of directing him to Lisa and fighting Lucifer. And thereby found peace and redemption. Well deserved, indeed.
I once was lost, but now I’m found,
Was blind, but now I see.