Believing Castiel was an angel wasn't the hard part. It was all of the other things that went along with that. Jason had grown up in a neighborhood some considered Hell on Earth. He tended not to rely on the divine to do anything for him. His basic world view took a cynical turn based on the knowledge that heroes fell, parents disappointed, and saviors didn't always make it in time.
Jason had no idea if it was better or worse that his soul had, according to Castiel, just been sitting around while his body had been six feet under. On the one hand, Heaven hadn't kicked him out. On the other, Heaven hadn't let him in, either. He hadn't been saved from Hell or stolen from paradise. He'd been a forgotten book on a library shelf, and who the hell knew who had checked him out.
Dean might know, he thought, then promptly smothered the idea. He didn't want to find out like that. He couldn't stomach the thought of learning about his resurrection as a story in a comic book. Hard as Jason tried to act like it was no big deal that his life was drawn and colored on glossy pages in someone else's world, he hated the idea that, if his life was just a story, some total stranger had wanted him to die, planned how it was going to happen, and then turned it into some sort of art project.
"Like I said, Cas. I'm not really hungry. Goes with the human thing when you're down in the dumps." Jason began breaking up the cheese and doling it out to his fawning canine public. "When you say I wasn't collected by a reaper, are you sure we even have those in Gotham? It's a different universe. Maybe limbo is where we all end up."