When Castiel says that the books are going to become the gospel of a new world, they always expected it was because they'd be able to save it.
They'd pop Lucifer back in the box and beat down the dicks with wings and fuck up the demons and just shoot every son of a bitch that thought that humans died easy.
(That was the plan. That wasn't how it worked out.)
They were so full of hope then, even if they didn't feel like it, and they thought they could be the heroes this world needed, even they weren't the ones it deserved. (Dean would like the Batman reference, if he were still around to read it.)
And then the Leviathans came.
They tried to fight, they really did, but Leviathans were worse than 'shifters, taking any appearance they so chose, and more ruthless, and they ate people.
They were everywhere and everyone and even though the Winchester's has always felt that the whole world was against them, it never really was, until the Leviathans.
And Cas was gone.
The angel, their ace in the hole, their friend, wasn't anymore. He was a Leviathan walking around in Castiel's skin, and it hurt all the more because Cas had been the one to set them loose.
It's not actually surprising how fast humanity fell.
Most of them are slaves (or food) to the Leviathans now.
There's no hope, no resistance, nothing except what the Leviathans want, because this is the Leviathans world now, and they're going to use it up until there's nothing to use up anymore, and after that, who knows?
But the Leviathans don't know that there is hope.
(Most of the humans don't realize it's hope, either. It's a story to tell in the dark, to keep the nightmares from their children, even though the nightmares are so very real nowadays.)
It's books.
Beautiful, heroic books, about The Righteous Man and his little brother, and how they fought and fought and fought, until they couldn't fight anymore, and even then, they still fought. For them.
They fought Heaven and Hell and Earth, demons and angels and wee beasties, things that the humans know all too well now.
There's hope in Dean and Sammy, the Winchester boys, even if they're not around anymore, because they've proved that, even against all the odds and things more powerful and evil than they could have imagined, humans can still be heroes.
They can fight.
They can win.
They can live.
(There are Sam and Dean girls again, even if they have to hide it from the Leviathans. There's fanfiction going around, about Sam and Dean and Cas- and not all of it is PG. There's a trend going around, of wearing denim and leather, even though it's so hard to come by.)
Humanity's not dead yet.
When Cas told them there's be The Winchester Gospels, they never even imagined this. But this is how it turned out, even if they're not here to see it. They're just doing what they've always done.
Saving people, hunting things.
(Spreading hope, when there is no hope.)
The family business.
- Chuck Shurley, Prophet of the Lord