Soulcatcher, book 4 of the soulkeeper series. The whole series is about these people who are born human but are given special powers from God. The last book (soulcatcher) is about these humans, and their ordinary friend, their trying to save earth from the devil and he wants to help. The special powered people don't want him getting hurt. In the end of the book he ends up saving the day. So even being just an ordinary human doesn't mean you can't do anything. (If you want to read the series it's called "soulkeeper" by G. P. Ching.)