Foster the People - I Would Do Anything for You Lyrics Meaning

The evidence is in favour of this being about God. The band has never directly spoken about their religious beliefs, and it wouldn't be completely out of the blue for them to be Christian.
For those in doubt about whether it's about God or a girl, may I direct you to the line, "Strange life I live, but it's what you decided."
You wouldn't say that to some girl. You would only say something like that to God.
I rest my case.