The real reason America is exceptional is, God is holding her in such a way. There are two other reason, one good and the other as good as it could be. The good one first.
I am honestly not sure whether you're trolling or not, but I've often found that a disturbingly large amount of Americans genuinely believe god somehow favors their country over others or that America is 'god's country' for some bizarre reason. They can never justify it other than blind patriotism/delusion but I always find it bizarre.