I'll take a stab.
I think Religion asked the question: what must I DO to become a child of God. I think it deals with quantity (i.e., how much), and frequency (how often) of the "goodness" that I would do so He would recognize me.
Faith deals more with relationships than actions. God makes me His child when I accept the salvation of His Son. Since I'm no longer bound by actions to get right with God, my attitude is more, well now that I'm right with God, and that I'm a child of His, how can I live a life worthy of that relationship.
As we all come from families, we all know that our parents love us often in spite of ourselves. We mess up, we disappoint them, we embarrass them, but we never think that by messing up, we lose our relationship with them. Because we love our parents, we want to do right by them, at least most of the time. It's different though from saying, I have to do right by them to get them to love me and be my parents. They ARE your parents, and will always be.
If the Christian God gives you an opportunity to accept Him thru faith, and you know you don't have to work for it, How would you repay Him? The answer is you couldn't, but you could live a life not to embarrass Him, and perhaps get to know Him better by talking to Him, reading and hearing what He has to say about Himself, you, and the plans He may have for you, which more times than not, are better options than what you would pick for yourself.
Not a bad deal.
