Purgatory is another of those things that the show completely mangled from its original purpose for the sake of the story. In this case, since the show’s mythos includes monsters, which the real world doesn’t, and they were too lazy to come up with a unique “monster hell” kind of place, they just slapped the name of an actual afterlife realm onto their made up construct, and for season 6 and 7 all the suggestion is it’s literally just for monsters, and they ignore absolutely all the actual lore about it.
REAL Purgatory is a construct pretty much of the Catholic church as a sort of waiting room before Heaven; a place where the kind of torment of Hell is dished out, but to penitent sinners who will one day be worthy of moving on to Heaven. It’s a transitional state and basically the biggest money making scam of the middle ages - the church sold you get out of Purgatory free cards and the more money you paid them for (I think they were actually called indulgences? I’m 3-4 years out of my Medieval history classes) the less time you spent there.
Basically: evil people, demons, heathens etc with no chance went to Hell, saintly people went right up to Heaven, but pretty much everyone else, even good Christians who’d done a few bad things - like being physically unable to uphold all the contradictory and impossible rules in the Bible, so EVERYONE - went to Purgatory on their way to Heaven. It worked like Hell does in Supernatural: because if you were a real dick but would one day be worthy of Heaven, you could spend literally a trillion years in Purgatory before Judgement Day, even though by Earth’s calendar that was always marked down as some time in the next couple of years as far as Christianity was concerned. In Supernatural it’s sort of funny to me that Purgatory seems to run on a normal calendar since I went into it with all this in my head.
All the punishment in Purgatory was believed to be for the express purpose of cleansing a soul, and “purgatory” even comes from the word “purge”. So when they say “it was pure” they are literally naming Purgatory over again without realising it.
However seeing as I had all this knowledge in my head when season 8 was airing, I sussed immediately that Cas *got* Purgatory so I read into it as literal Purgatory the whole time that season. He wanted to stay as a punishment, and he even talks about penance a lot, and it’s basically all he actually wants out of the season after he’s yanked out of Purgatory. I can tell that the show couldn’t actually go around and change Purgatory into the Christian Purgatory because the monster lore was already written into it and they can’t retcon something so wildly. So, no humans on their way to Heaven. But it absolutely served its purpose metaphorically.
I think each character went in there with their own penance (let’s ignore Benny since he’s awesome and all but a monster and their souls are trapped in there with no chance of escape - his “it’s a human portal” line is one of the biggest things that tipped me off, aside from Cas’s attitude towards Purgatory, that they were subtextually using it as Real Purgatory).
Basically, Sam’s easy: he walks in and out in a day and doesn’t even spend all his vacation time on Purgatory. Season 8 was bookended with Dean guilt-tripping Sam about not looking for him and Kevin and then all the stuff he throws at him when talking about Sam confessing, but Sam admits there was only 1 thing he truly felt he needed to confess to. His penance was something that still lived on Earth, and therefore there was literally nothing that Purgatory could offer him in the way of cleansing his guilt/sins, especially as he was *already* on a God-level cleansing mission when he went in there. So, he got spat out immediately. I think it’s important that he had to use the portal despite going in there not thinking he had to: it sort of shows Purgatory willingly disgorging him and telling him there’s nothing for him to be ashamed of.
Cas chooses to stay in Purgatory, and he alone actually understands its purpose: he knows it’s purifying him, because he was crazy before he went in and sane the moment his feet hit the floor. It’s like in LOST where Locke knows something’s special about the Island because he was in a wheelchair before but could walk the moment they crashed (the LOST island basically was Purgatory metaphorically as well and whatever the show went with it was such a popular theory because it was also serving the same purpose for its characters). Anyway. Purgatory immediately removed the blockage to Cas facing what he felt were his greatest shames: not long before he’d been trying to apologise via boardgame and was told “You’re just playing sorry” and oh my god, once you’ve read my headcanons on Purgatory go watch the boardgame conversation with Dean and see it through this filter, it’s FANTASTIC.
Anyway, he can understand what it’s done/doing for him, and of the 3 characters he’s definitely done the worst in sheer numbers/awfulness scale. He’s never been given a real chance to atone for season 6; what he did with Sam and the hell visions only scratches the surface of the problems *just* between him and the Winchesters, while there’s also the entire universe holding a reckoning against him.
When Naomi pulls Cas out, she has this hold over him and while she lets him run free to continue his penance, of healing and helping where he can, I’m sure her hold was so strong because of the guilt trip, and her stepping in as a sort of proxy-Purgatory. Her missions were meant to be an atonement - she pulls him out of Purgatory to start using him for her own ends. Cas breaking the connection can be seen as him also finally having Purgatory let him go: by not killing Dean and realising what it genuinely important to him, by *choosing* between Heaven and Dean, he understands where his heart lies, and for the first time he can even begin to come to terms with his guilt for breaking Heaven, because he’s realised there is something more important. Once he realises that the need to atone drops away a little, and while it still motivates him right through to at least the end of season 9, he’s beginning to draw away from that and let the guilt go piece by piece, judging by how much easier it was for him to pick Dean at the end of 9x22. As he was taken out of Purgatory before he was ready, though, it’s much harder for him to let go immediately.
Now, Dean in season 7 is a wreck we largely agree was caused by the end of season 6 and not stopping Cas; his season 7 guilt trip gets worse when he kills Amy Pond because he sees her as a proxy-Cas: he can stop her before she kills again when he couldn’t stop Cas, but that just leads to it eating him up more. With the judgement episode in season 7 we’re basically getting Dean coded as guilty as hell, and most of that is goes right back to his Cas trauma even if the series never directly addresses it. So although he begins to get over that towards the end of the season once Cas is alive and heals Sam, Cas is crazy too much for him to have the 2-way conversation he needs to have to finish the forgiveness/letting go of guilt process. He goes into Purgatory weighed down by Cas. I think it’s also important that Sam has no magical narrative attached to him before this time: there’s nothing worrying about him compelling Dean to go back, and it means the narrative squarely puts his issues he goes to Purgatory for on Cas.
We see a lot of comments that Dean was willing to stay in Purgatory and look for Cas instead of hastening it out of there to find Sam. I think it’s not that simple, if we assume Purgatory is being sneakily written as literal Purgatory; like I said in those tags, I don’t think Dean could have left. He needed to find Cas, but more importantly, he needed TIME to find Cas. Cas bolted, yes, and he probably had no idea, but I headcanon that Purgatory deliberately kept them apart for the year. Dean’s guilt/sins aren’t so big that he needs to spend more than a year there, since Purgatory apparently runs in real time, but he needed that time to come to terms with why he was looking for Cas and what that meant to him.
There’s a ton of amazing meta out there on the bit where Dean finally finds Cas, but the important thing is that he was totally willing to hear him out, even stopping Benny for bitching Cas out about running off. He offered Cas home and friendship and a hug. Everything from season 6 is forgiven unconditionally at last. When Dean says he can’t leave without Cas, he MEANS it. Whether his subconscious or something Purgatory suggested to him, he can only put things aside and leave if things are good with Cas, if Cas is coming home. Cas, like I said, understands Purgatory better because he’s an angel and if it’s not lore they know it’s something he intrinsically understands from being there. He can’t argue with Dean about it because Dean’s journey of recovery turns out to be via Cas.
When they get out and Cas stays behind, it breaks Dean, and that break can only be resolved when Cas shows him the truth. Like Cas, Dean leaves Purgatory a little broken because he didn’t wholly finish his penance, but Cas being back fixes it, and from that point on we get happy season 8 Dean for the middle of the season and it’s glorious, because we’re seeing him with all the weight on his soul scraped off. I think if Cas was Dean’s penance, he needed to come up with the fake memory not just because he couldn’t imagine Cas not wanting to be with him, but because of the way it undermines what he worked for for the whole year and destroys his whole mission, and therefore invalidates the cleansing he underwent there. It’s safe for him to find out how it really happened once Cas is actually back because, well, Cas is there, and that’s what he worked for. His comments on Cas getting out, though, do suggest that he knows it’s very wrong that Cas is out; he niggles at it until the truth comes out, and I think he could sense in a way that something about his Purgatory experience was still being undermined.
Basically, Cas ensured Dean got out by tricking the system. He knew Dean couldn’t leave without him but he knew his penance wasn’t over. So he let Dean believe he was going, right up literally until the last moment. It bothered me at first a little why Cas would go right to the portal with Dean but this makes sense. If Dean knew he wasn’t leaving the guilt would be back on his soul (as it was when he left and Cas didn’t), and therefore the portal would not deem him ready to leave and refuse to let him out. A catch 22 only solved by Cas lying to Dean while they were together in Purgatory and letting him think he was leaving with him.
Still, however messed up they were after, they both went INTO Purgatory in a much much worse headspace - even Cas in the brief moment where he had his memories but before he cured Sam was in a lousy headspace, hence doing something so self-destructive for the sake of making amends in the first place. So when they come out the other side, they were legitimately purified by Purgatory.
