JC's best friend (let's call him A) asked me that question yesterday. His parents are raising him in a Unitarian Universalist Church - they describe it as "believe whatever makes sense to you" and there appears to be quite a range in their congregation, from naturist to atheist to Christian. They were raised Christian (him) and Jewish (her), but this is what works for them.
It's interesting sometimes, because we attend church (Methodist) regularly and are active in the church. So are they. But clearly this has raised some questions for A. Although he probably knows more about different religions than my children, clearly that fundamental aspect of faith is hard for him, and his church doesn't have a belief system except to respect others (as best I can tell).
How do you explain faith to an extremely bright and logical 14 year old? How do you reconcile that fundamental difference that I, an (over)educated engineer, a believer in science, believes that evolution is true and also believes that God created the Universe? As far as A is concerned, there is no proof of God's existence, and that leap into faith is incomprehensible. And of course, trying to be truthful with him makes me think about all the aspects of faith that I do struggle with, from the literalness of the Bible (I'm of the inspired camp myself) to the necessity to believe in Jesus for salvation (I have a hard time condemning non-believers outright).
But that's religion, and I think A is really looking for an explanation of faith. And faith, well, I can define faith (my favorite is "Believing without seeing"), but how do you explain faith? How much of my faith is truly believed and how much is learned habit (see how this is hard for me?)? I know part of A's problem is the representations of religious people he sees in the media. Face it, some of the "Christian" rhetoric out there makes me wonder if they ever read the Bible. But I will continue trying to explain, and talking when he wants to listen, and listening when he wants to talk. Because perhaps this is why God has put me here with this child at this time, to teach him at the very least that God is working through some people, and that people of faith can be kind and considerate and smart. It's going to be an interesting road.