To understand how this episode does this, we must first look at the Werther Box itself.
How did this vestige of the Men of Letters come into existence? What was its purpose? And why are Sam and Dean going after it now? After all, it was created over fifty years ago. Dean points out to Sam that this case isn't simply a cold one, it's “sub zero.” There's little reason why either one of them would have any interest---far as Dean knows---in digging up such an old case.
In the flashbacks, however, we see that Magnus aka Cuthbert Sinclair had designed a particular box to protect a very particular object. This was to prevent a Codex from entering the hands of the Grand Coven. Its spell work and ability to decipher magical texts was far too dangerous for the witches to get their hands on, and so the Men of Letters killed its creator and assigned the task of protecting the text. To do that---meaning they had to have a spell that the Grand Coven couldn't simply override---Magnus came up with the Werther Box. It would contain this text, keeping it out of the Grand Coven's hands and keep everyone safe from their evil magics.
Only there was a problem with his solution. It, as he stated proudly, had a “98% lethality” and it had cost the lives of two Men of Letters. They were trying to open the box, to obtain its contents possibly to catalog or bring the Codex into a Bunker---only the spell work he devised to protect it killed them both. It lead the Men of Letters to charge Magnus with their deaths, and in his expulsion hearing, they demand to know how to disarm the Werther Box. Magnus refuses, and he ends up telling them that one of the Men of Letters that died---Martinez---was on the right track. He did die by the box, with his wrists slit, after all.
But how does the Box kill? We see, in 1973, a family living in a house. A young girl is forced to finish the laundry for her mother, and in retaliation, she goes into the basement and smashes open a wall. It's there that she encounters the handiwork of Magnus, and the Box is reactivated after being dormant for so long. When she comes to, she sees that everyone in her family has succumbed to something. Her father has shot himself to death, her brother hangs himself in front of her, and her mother slits her own throat. No one, but Suzie, survives. His spell work to protect the Codex inside worked flawlessly, and did kill with his exact percentage rate.
Sam trips over this case when he makes his deal with Rowena. She'll help him crack the Book of the Damned if he'll kill Crowley in return. To do that, however, she'll need the Codex the Men of Letters killed her friend Nadia to obtain. To get it, he'll have to search into the files and find where they may have put it. It's there that he stumbles upon the Werther Project. Immediately, Sam wants to find this book, all in hopes that he can bring them closer to the cure for the Mark of Cain.
But he doesn't do this case solo---as he had planned. Instead, we see Dean join him, and it's his solo we'll look at first.
After Sam fails to break into Suzie's house---complete with her gun pointed at highly sensitive areas through her mail slot---Sam returns to the car to find Dean waiting. His brother apologizes for going after a six member vampire nest solo, calling it a “douche move,” but wondering why Sam would be going after this extremely cold case alone. If it's to punish him or teach him a lesson, Sam need not do so. He gets it. He tells Sam, “If you say this is a case, I'm in---if you'll have me.”
So, Dean decides to go back to the front door and talk his way into Suzie's house while Sam goes to the back. He keeps her mostly distracted, although a few minor bumps in the basement outs Sam and Dean's ruse and Suzie demands that Sam come upstairs. In this moment, Sam's spell---given to him from Rowena---fails, and the Werther Box reawakens after thirty years of dormancy. The green and black smoke of its spell winds up and through the room like eerie tendrils, instantly possessing both Dean and Suzie where they stand.
Dean encounters Sam after he rushes up the stairs, and Suzie chases them from the room, waving her gun, Gus, after them. And yet, Dean stops in his tracks, finding his reality blurring. One moment he's in her cluttered house, the next he's facing the harsh and unforgiving landscapes of Purgatory. It flashes back and forth until finally he finds himself attacked by a Leviathan, trying to fend off the killing blow. A familiar face comes to his rescue in Benny, and the vampire and Dean start to make their way through the trees.
While the Werther Box pushes its victims to hallucination, Dean realizes immediately that he's caught in one---telling Benny, “You ain't Benny---I'm bummed out, too. But you are just a figment, okay, you're subconscious junk my brain's throwing up to distract me from getting back to reality.” He trudges ahead, trying to put distance between himself and his friend, hoping he can find the exit and soon. After all, admitting that he was facing a hallucination should have snapped him from this. It doesn't, and Dean finds himself repeatedly making the same circle within Purgatory. Running away from Benny, running away from this place, and running away from what the Werther Box is trying to make him face is not the answer to breaking its powerful hold.
In the outside world, Dean is extremely immobilized. He's largely frozen in one spot, staring blankly ahead and mumbling his brother's name---among other things from his hallucinations. Dean's so far-gone that he's able to be tied into a chair---seemingly without resistance.
As Dean stops and finally confronts Benny in the hallucination world, he tells his friend that he needs to get out. Benny retorts, “Need and want are two different things, ain't they?”
Much like Sam tying Dean up in the real world, Benny's statement freezes Dean in his tracks. Now, he'll have to face head on some of the things he's been hiding or running from lately. He'll have to acknowledge some of the truths he's tried to cover up with bravado. He'll have to face the Werther Box's test and find a way to not only overcome it, but to overcome himself in order to do it.
Benny asks him, “You gotta wonder, why this figment? Why this place? ” It's a great question. Purgatory is pure. It's full of monsters and it's “360 degree combat” seems to fit so well with Dean's current needs. After all, he did go after the vampire nest by himself. He may have texted his brother to join him---and yet he couldn't wait. His reasoning was he “needed to take the edge off” and so he went for it. Now that he's surrounded again by the nature of Purgatory, Benny points out to him, “This place, you don't have to go looking for a fight. All you have to is be still for one moment, and that fight will come to you. That's why you're here, Dean. That's the purity you crave -- killing with no consequence.”
This concept is rather appealing to Dean. He's been struggling with the Mark and its pull to murder. He's had it humming in his ears, pushing and pulling at him at every turn to sate its blood lust---something he'll never do because it will always want more. Each hunt that he takes on increases the chances he may finally crack, may finally give into its dark power. Dean knows that it will only get worse from here on out. The vampire nest he eliminated proves this truth.
But to stay in Purgatory, to give into this illusion cast by the Werther Box would be freeing him from that fear. It'd be allowing Dean to kill and indulge the Mark with impunity. He tells Benny, “Good a place as any to call it day.” Why keep fighting out there when you can fight without tethers forever in here? Why not give in and take this gift? This place would allow Dean to relish in the hunt, to fulfill the kill, and to do it again and again without ever having to harm anyone ever again.
Beyond knowing that he has a desire to kill, a need to fulfill the Mark's endless blood lust and that it will never end---Dean knows that he also has to face the truth that his plan for when---not if---he loses to the Mark has flaws. He baldly told Castiel and Sam that they were to take down anything that came out of the room when he faced Cain. He meant it. If he had lost to the Mark and emerged as the demon or worse, they were to take him out just as he was sent in to take out Cain. It would seem that Dean's held onto that request---that demand---ever since. He wants them to follow through on that promise when he should finally fall to the darkness he knows is surely waiting to reclaim him.
And yet, Benny points out to him that it's folly. He tells Dean, “You gonna get Sam and Cas to pull you down? You really think they're gonna keep that agreement, come on. Dean, let's say they do. Do you think they'll ever recover from that? It will ruin them.”
Dean already knows and understands this. What the Werther Box is doing is pulling up things he buried under everything else. It's throwing it back in his face, and reminding him that this plan to have his brother and his friend end him if it should come to it will end only one way---badly.
Benny shouts at him, “Maybe kill a few humans? Kill Cas? Kill your brother? Yeah, that's mighty honorable!” It's another acute fear that Dean hasn't been able to hide from nearly as well. We see it in the nightmares we know he has. We know the words Cain left him with about killing Crowley, then Castiel, then his brother---the one he'd never survive---haunts him day and night. It's also a fear Dean must face here and now if he has any chance of snapping out of Werther's hold.
Benny gives him a solution to fix both problems. The solution means he'll never have to hurt anyone ever again---and he'd never have to make his brother or Castiel face the hard task of putting him down like a vicious monster. Benny tells him, “No one needs to know, Dean. What happens in Purgatory, stays in Purgatory.” He's giving Dean the option of staying here. He's opening up the choice that Dean---by accepting the brutish Purgatory weapon---can end it here and now. He tells Dean, “Out there, you're sleeping. You make the right choice in here and you'll sleep forever and you won't hurt anyone ever again.”
Dean hesitates, holding the weapon close. He examines it. In the waking world, he snaps out of the ropes Sam tied him into the chair with, pulling himself towards a counter. A bottle fits into his hands to stand in as simile to the weapon he's holding in Purgatory, and he smashes the bottle preparing to end his life in the physical realm as much as the hallucination world.
But he can't do. Dean stops, and admits, “I'd do it, if I really had to, I would.” He knows that this is an option he's had to consider and dismiss, and he must do so again here if he has any chance of breaking the spell.
It's more than that, however. Dean has been feeling despondent for so long, forced to face that the Mark of Cain is a terminal disease that he cannot escape. It's hard to blame him for this viewpoint. Cain has confirmed it as such. No attempts to finding a path to a cure have come to any fruition, and Dean has had its dark power slowly sap on him for months since the demonic cure was administered. In many ways, Dean sees no chance of himself coming out on the other side intact. That being said, he must face this attitude. He tells Benny, “Even if I could, this wouldn't let me,” and the Mark, even in this hallucination glows bright.
Dean must face the Mark and he must face the fact that he's allowed it to make him give up recently. He has to remember why he's fighting, why he can't simply accept this offer from his subconscious at the behest of a spell. For so long, he's chosen to reclaim his life from the Mark by pretending that it wasn't there, that he'd go back to indulging his habits for food, drink, and more. He'd go down swinging instead. This is a healthy tactic to take---but only to a certain point. He's standing at a crossroads here in this Werther created illusion. Either he accepts that the Mark and its dark possession is inevitable, or he does something about it and fights back to keep going and stop it. Either he just waits for it to reclaim him little by little and accept that as fact or he tries harder to find the fight to resist.
Most of all, Dean learns that he doesn't want to die---and in turn he doesn't want to wait for the Mark to win out over him. He's reminded that he must fight it and fight back now or never. And as he sinks the Purgatory blade into Benny, Dean snaps the spell to find himself in Suzie's house, holding the smashed bottle. Instantly, he rushes to the basement, hoping he's not too late to save Sam.
Sam's solo is just as crucial. He, too, must face the Werther's hallucinations. It, too, will force him to experience everything he's suppressing. All the doubts, the questions, and the desperation that has marked him lately will rush towards him in this experience. It will force him to confront himself and what is happening. It will make him see why he's doing what he's doing---and why he, too, must not give up in the end.
In the beginning, when Rowena informs him that she can't read the Book of the Damned in its present form, Sam starts to stop their negotiations. Knowing she has him at a severe disadvantage, she says, “Desperate. You can stop pretending you're not.”
She gives him the information about Nadia, about the Codex that will allow her to read the book, and Sam agrees, clearly driven to do whatever he must in order to get what he needs from the witch. He also refuses to acknowledge her comment, even if his facial expression gives him completely away. It's this denial of his desperation that will come back to bite him later on.
After he uses her spell to try and break the spell Magnus uses, it fizzles out. Sam had been rushed and flustered after Dean inserted himself into this case. After all, he didn't want his brother involved in on it. He didn't want his brother to know why he was really doing this. Dean threw him off a little, showing up to help him with it. And as he's down in the basement, using the spell Rowena warned him would fizzle out, he's further distracted by Suzie's outburst. It causes his flame to go out, and as he twists the door on the Werther Box, he inadvertently triggers the magic Magnus left behind. Even if he had been able to enact the spell exactly, it's likely that it would have failed anyways. Magnus designed the Box to open only one way, after all.
While we see the spell slam into Dean and Suzie, we're struck by Sam's first encounter as he rushes up the stairs. Once they've run from Suzie, Dean accuses him, “You don't have a plan! You don't have a defense!” It's possible that this accusation may be Sam's first hallucination. It's possible that, as we see the point of view shift from Dean and Suzie to Sam, that he's encountering an image of his brother here. He has no idea, yet, that the spell has enchanted Dean. We don't know if Dean's trip to Purgatory and subsequent physical immobilization happened instantaneously. But it's a clue that perhaps what Sam's seeing might not be as real as he thinks.
After all, as Sam rushes to the door to get to Suzie, he shouts for his brother, only to receive no answer. Frantic to get through to her before it's too late and distraught by his brother's lack of answer, Sam wavers on what to do. He begs Suzie to let him, the door not giving way. This door, in his hallucinogenic mind, may have been held solid against him. The spell may have led him to believe he couldn't open it until the fatal shot is fired and he knows Suzie has been claimed as another Werther Project victim. Afterwards, it swings open and Sam enters to see Suzie dead to his dismay.
It's here that his solo takes on his inner fears, doubts, and questions. Suzie's “ghost,” a manifestation of Sam's mind, throws up his harshest doubts, questions, and criticisms of himself back into his face. It brings up his guilt, twisting it deep into him. All of these things are healthy things to possess. After all, Sam has to have some questions about what he is doing, who he's working with, and why he's doing what he's doing to save Dean. He has to wonder if this is the right path. It's something he must tamp down frequently, knowing he's chosen to do this and ask for forgiveness later when he's succeeded in his goal of saving Dean.
But Sam has to face it head on if he's to acknowledge it, too. Suzie shouts at him, “A lot of good sorry does me, look at me. Look. At. Me. There she is, the first casualty in your misguided mission, but what's another human life to you? Any thing's worth it, as long as you two make it out alive. And how's that search going? Any closer to a cure?”
Sam recoils from this---the guilt and the doubts---but immediately asserts, “This isn't real. You're not real.”
The Werther Box won't let Sam go that easy, pushing him further. She asserts, “You think Dean's the wild card, the loose cannon. But don't you see? Making deals with with witches, opening Pandora's Box down there. You're the reckless one. You'll do anything to keep clinging to that doomed brother of yours. How many more will die, Sammy? You know it. You have to be stopped, and the only that can stop you is you! Do it Sammy, end this farce once and for all! ”
Not unlike when his hallucination of Lucifer pushed him to kill himself, the Werther Box is trying to push him to that awful end. It's his doubts and fears about what he's doing coming to a grim and terrible head. While these questions may be healthy in the light of day, without the influence of this dark magic, here they are twisted into a terrible and frightening conclusion. And yet, Sam can't give in. Killing himself to stop his search for Dean's cure won't solve anything. Not really. After all, if he should follow through and his brother should succumb to the dark power of the Mark, who will be able to stand against Dean then? Who will fight harder to save Dean and everyone from the dark power of the Mark than Sam?
Just as he's wavering about giving in, another hallucination takes hold, and “Rowena” arrives to dispel Suzie's dark doubts. “Rowena” is no different a bed fellow for Sam's hallucinogenic mind than Lucifer was when Dean disappeared in “Repo Man.” There, too, Sam relied on his hallucination of the Devil to save his brother, to push through his doubts and fears to complete the case. “Rowena” represents that same powerful emotion in Sam here: his utter desperation at saving Dean.
It's clear when we see her push him to go back into the basement, to show her the box, and to start to figure out its secrets. Much of the information he uses to crack its terrible code is already trapped in his mind. It's fed to him through the guise of the centuries old witch as she uses her “magic” to illuminate the elegant script inscribed around the door on the Werther Box.
Sam reads the inscription, realizing that Magnus had given the Men of Letters the answer in the minutes of that long ago meeting. He had told them that Martinez was on the right track. Sam, reading the words “the blood of our own” realizes that Magnus designed the Box to only open for Men of Letters members. It would never yield to a Grand Coven witch determined to reclaim what they had had taken from them. No spell---including the one that the real Rowena had given to Sam---would crack its code. The only thing that would open this Box and grant them access to its contents would be for a Men of Letters---or a legacy as Sam is---to bleed for it. Their blood would trigger the spell to break. Only then would they “silence the Werther for good.”
Sam, desperate to get into the box, quickly takes the bowl he used to make the ill-fated disenchantment spell, and sets it by the Box itself. “Rowena” is curious about his behavior, giving Sam's inner doubts yet another voice when she asks, “How do you know this will work?” Sam simply answers, “I don't.” It's this acknowledgment that is crucial. Sam knows that even if he should get this Codex, even if Rowena should crack the Book of the Damned wide open, the cure it provides may be yet another terrible dead end in his quest. But, Sam is so desperate and he knows the only way to truly find out the answer is to try.
So, Sam slices into his arm---unaware that the key to opening the Box is also the Box's attempt to kill him. It wanted him to kill himself, to stop himself from going too far in his quest. It wanted him to die before another could become a casualty in his desperate search for a cure. Now, it feeds into Sam's other drive to die to save his brother if necessary. He allows the blood to trickle from his arm into the bowl, and finds to his astonishment and joy that the Box starts to react to his offering. He will manage to open the Box. He was right---and the hint that Magnus dumped on the pompous Men of Letters back in 1956 comes back to help Sam break the spell---almost.
As the cut stops spilling his blood into the bowl momentarily, Sam finds that the Box loses its glow. The power to stop its evil magic ebbs and he's back to square one. Knowing he has to be on the right track, though, Sam slices again, giving the Box more of his blood. He's falling further into its trap to save Dean---all by sacrificing himself. “Rowena” eggs on him on, telling him, “It wants more Sam. It wants all.” Sam gives in, stating with utter desperation, “The Codex. The path to the cure. It's in there. If it wants more, it'll get more.”
It's key that Sam experience this desperation to this level. It's crucial that he endure this so he knows just how far he's willing to go and why that is folly. His dying upstairs when faced with Suzie wasn't the answer, and his dying down in the basement, even if it should open the Box, isn't going to solve anything, either. His dying in either scenario would leave his brother alone to deal with the Mark. It'd leave Dean vulnerable to do so. To die here, even if it is to get to the Codex he's after, would prevent Sam from achieving his ultimate goal. He can't save Dean if he doesn't live.
That's the very thing Sam must take away from this experience. No matter what it comes down to in the end as they finally find a way to crack the cure from the Book of the Damned or find some other method, Sam has to live if it's going to mean anything---or if it'll actually save Dean. His dying could send his brother over the edge. His dying wouldn't stop the Mark from completing the process of reclaiming Dean for good. Sam has to stay alive in order for Sam and Dean to best the Mark---together.
It's that togetherness that becomes the ultimate answer and revelation in “The Werther Project.”
As Sam is slowly bleeding out, giving into the dark hallucination that the Box provides, Dean rushes in and gives his blood alongside Sam. Their combined legacy blood---and proof that perhaps Magnus meant two Men of Letters must give their blood to break it---ends the terrible spell. It glows a bright and brilliant gold, flares, and allows them to swing it open. “Rowena” dismayed at her failed attempt at killing Sam fades away with a resigned, “Ah well.”
As the brothers make their way into the Impala to drive back home, Dean remarks, “The universe is trying to tell us something we both should already know. We're stronger together than apart. ” He's amazed that this Box managed to throw them both into solo hallucinations that nearly cost both of them their lives. It's in this separation that they were nearly destroyed.
And yet, they had to endure these solos to come to the conclusions about their shared roles in their long enduring duet. They had to face their own fears, their own doubts, and come away with an understanding that they are both in this together. In their own ways, Sam and Dean did just that. Some of these revelations will take time to settle. Some of them will take time to be fully realized. Others they had to face here and now if they were to cut through them and get past them for later on.
Sam returns to the real Rowena, Codex on the table inviting her to rush gleefully towards it. Sam learned well from his experience under the Werther Box's influence. As she tells him that she can indeed use this book to read the Book of the Damned, Sam pounces. He grabs her wrists, chaining her with pure iron to hold fast her magics, and tells her that this action is, “Insurance.” He faced his doubts about working with her. He knows that he's still risking much to allow her to read either texts, but he will use her and then destroy both books when he's gotten what he needed.
He tells her, “I'll burn the Book.” This frank statement is crucial. Dean did want the Book burned in the first place. His statement that he'll do just that after she's garnered what he needs means he is willing to go along with that wish. By stating this, he's coming to terms that no matter what he's hiding now, in the end, he and his brother will have to do this together.
After all, it's the only way they'll ever overcome the Mark, Rowena, and whatever other enemy may come against them.
In the end, Sam and Dean must always keep fighting----together.