I know in some stories it's been established that gods only have power as long as mortals belive in them. The DC Universe works that way, at least according to Wonder Woman, I think. The more followers they have (and probably the more devout they are) the more powerful the gods can be. If they have no followers, they fade away.
So here's what I was wondering, and I think it's a bit of an inversion of that. Have you seen a story where a god attempts to aid, harm, or interfere with a mortal, only to be unable to do so because the mortal doesn't believe in the god in question? It isn't a case of the god being completely impotent, they would work on a believer, just not on someone who doesn't believe. Granted, there's a chance of the god coming off as useless, but I think you could show the god using a believer to accomplish their wishes. You know, the god appears to them in their morning coffee and tell them they're needed, or gives them a power boost so they can do what needs to be done.