Aziraphale had tried to explain it to him once. The whole point, he’d said - this was somewhere around 1020, when they’d first reached their little Arrangement - the whole point was that when a human was good or bad it was because they wanted to be. Whereas people like Crowley and, of course, himself, were set in their ways right from the start. People couldn’t become truly holy, he said, unless they also had the opportunity to be definitively wicked.
Crowley had thought about this for some time and, around 1203, had said, Hang on, that only works, right, it you start everyone off equal, okay? You can’t start someone off in a muddy shack in the middle of a war zone and expect them to do as well as someone born in a castle.
Ah, Aziraphale had said, that’s the good bit. The lower you start, the more opportunities you have.
Crowley had said, That’s lunatic.
No, said Aziraphale, it’s ineffable.
Aziraphale. The Enemy, of course. But an enemy for six thousand years now, which made him sort of a friend.