Preacher (Comic Book)/WMG

Preacher is a bubble universe
It had to be contained in a bubble outside the "real" universe-which is why it is somewhat fucked up-due to the negative resonance feedback event (apocalypse) that would caused by the Saint having Enuff Dakka if they were released into the universe proper.

"God" is actually Lucifer.
Let's see. He introduces himself as "the lightbringer." The devil that the saint killed was clearly a demon, not a fallen angel. The devil was also an undereducated coward. "God" needs to be loved and created the devil simply as an unrealistic villain. "God" definitely displays the sin of pride. The universe he created actually doesn't make that much sense. An organization of religious zealots apparently control every government in the world. People may be weird in the real world, but no one is as messed up as some of the characters in a universe created by Lucifer. So Lucifer loves God, but God loves humanity. Lucifer rebels and is cast out of heaven. Lucifer then creates the universe in which Jesse lives and declares himself "God." It is similar in many respects to the original universe, but not exactly the same. And of course the sin just fits too perfectly.
 * He also calls himself the morning star. To be honest, I almost accept this as canon.

The whole series is just the insane delusions of Jesse.
My theory is that he snapped when his church collapsed and he imagined the whole thing.