God really was telling them to do those things. If you remember earlier in the movie, when they are going to kill the fat short guy who kills little girls, the dad says that god will blind other people to what they are doing. At the end, when you realize that it was Adam the whole time, the video tapes at the polie station are all messed up so you can't see his face. And the few people who did see him, can't remember what he looks like.
Another point being that the Angel comes to the dad and tells him that Fenton is a demon. Of course at the time we don't know that. Then when he is older, Fenton ends up on the list which is why Adam kills him.
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