One of the things I loved about 2e (and especially Planescape) was that the gods gained more power if they had more believers. This does present an interesting paradox, though.
If a good priest is trying to get his congregation riled up to fight the forces of a demon, he has to convince them that the demon is powerful enough to be a threat. While this certainly works to get his followers ready to fight, they have to believe the demon is powerful or they won't bother. Therefor, they are granting the demon more power, because they believe in him.
I just think this is kind of funny, but pretty awesome, as well.