Well, the problem is that if God gets involved, the story is over. He wins. So you have to keep him out of it. In ROSEMARY they do declare God is dead, maybe they're not just saying that.
When I was writing THE DESCENDANTS for Dark Horse (not the Clooney one, for those who don't know this story), which was about the descendants of angels (fallen and otherwise), this bothered me a lot. I tried to hang a lantern by having a character in the obligatory secret organization mention that God isn't actually infallible, but they want the world to think that so there's not a panic/anarchy. Boy, did that ever not fly.
Ironically, believers have less trouble with this construction because it's the way they believe real life works. The devil has free rein, we have to oppose him as best we can, and God doesn't get involved because free will or faith or something. REASONS, OKAY










