Both God and the Devil stepped in to help him become the person he truly was inside. To realize his "inner self", which was actually a combination of all of the aspects of his wishes.
His inner self was powerful (drug lord), sensitive (beach guy), smart and witty (the author), athletic (basketball)and at the end he showed he was caring enough to give away his last wish. Each aspect taken to the extreme was what went wrong, but a little bit of each incorporated into the whole being is the balance he was looking for at the beginning and ultimately made him a better person.
Once he realized that, he was happier with himself and that opened the door to meet the woman of his dreams-- Nicole.
I think that the Devil and God are both working together to bring out the best in humanity. God entreats us to be altruistic, and the Devil tempts us with selfishness. It is up to us to rise to the challenge or fail.
— Dragndex, in an IMDB.com comment, Saturday, 5 Dec 2009, 10:11 CST.