the "devil worshippers" in the end are chanting: "banana bread, banana
bread, banana bread."
i guess thats a petty clear statement on how you shouldn't just jump to
any kind of explanations isn't it?
If they were chanting banana bread, it was because in the beginning of the film, Cotton said he could get his congregation to "hellelujah" to anything - so he talked about how to make banana bread. And sure enough it worked - everyone said "hellelujah!"
So to me, at the end, it's referencing that the demon had targetted Cotton from the beginning. Either that or everything is faked (Cotton's lack of faith and therefore colluding with the townsfolk to make a movie to prove what he tells the camera he doesn't believe in). Or it's juat a dream.