I used to frequent a discussion forum that was a safe haven for disgruntled ex-churchgoers and seekers. The range of discussion there was fairly broad, and pretty much any belief was fair game. The last part of my tenure there, however, saw a shift in discussion with the increased visitation by atheist posters. In and of itself, this wasn't a bad thing. I'm not one who turns up his nose at people who don't believe as I do (if I can help it, anyway), and while I did go through the same phase that most Christians go through where I parrot any number of explanations for why atheists don't believe in God (They're in rebellion, they're human-centered, they're holding a grudge or whatever), I've found that once I let them tell their own story, these explanations and categories don't work so well.
Anyway, back to this discussion forum. Like I said, a growing atheist presence was not in and of itself a bad thing. However, for a time, it seemed that every discussion inevitably would degenerate into the same basic argument: whether or not God exists. I suppose that I shouldn't have been so amazed or surprised that we'd always wind up talking about this no matter where the original thought began, but it became repetitious and I didn't find much meaning or use in it after a while.
I gave up trying to "prove" God many years ago. For me the reason was pretty straightforward: you can't. That's what faith is all about. Anslem, Aquinas, down to more recent e-mail forwards have lifted up various explanations of how one "knows" God exists. Some such as C.S. Lewis have tried to argue from the position that there is an innate sense of morality within us all and God put it there. And of course multiple creationist theories find wide acceptance among Christians. When it comes down to it, I'm a creationist. By definition, all Christians are creationists. I'm just not a "6-day" one. And passing belief off as science raises some red flags for me as well.
Here's why I give up trying to "prove" God. How often has a reasoned discourse on God's existence brought anyone to church, temple, mosque, etc.? How often has a dissertation on God's nature changed a mind, let alone a heart? I'm willing to bet that in the vast majority of believers' cases, they didn't decide to take on a dedicated life of faith because Anselm's proofs convinced them. And when speaking of these things, I also automatically exclude those who have been bullied, shamed or otherwise coerced into "believing" by any religious institution. In those instances, it wasn't the argument that convinced them...it was something else. In the same way, usually it isn't the argument that convinced those who have come to believe. I place tradition, upbringing, and personal "Aha!" sorts of moments all way above being rationally convinced by any sort of creationist argument. People who become Christians have either claimed their family's churchgoing ways for themselves or have otherwise felt moved by some sort of spiritual wind that caught them in just the right way and at just the right moment. After that and only after that might one visit different rationalized discourses and say, "That makes sense to me." It still might not make sense to an atheist, though.
Well, what's this really about? I'm a Christian. Not only by definition am I a creationist, but to many atheists by definition I'm a fool. Why bother with all these inconsistencies both in scripture and between belief and the way the world really works? God is love? Tell that to the families of the tsunami victims. What's your explanation of the theodicy problem? Why is my wife dying? Why should I bother with your God, let alone anyone else's?
You won't find a simple catch-all answer in this post, so if that's what you're seeking, I'll save you the time. The standard answer that I give for why I believe is that I base that belief primarily on personal experience. I truly was within a hair's width of giving it all up and got reeled back in. So then the questions flow: why'd you get an experience and I didn't? How do you know the God you experienced was the Christian God? Why's your experience true, but this other person's whose experience is in direct contradiction to yours but is believed to also be authentic, not?
Assertion and deconstruction. This is typically the way the conversation goes, and it can only go so far. At this point, the entire debate seems like a waste of time to me. I believe because one night I gave up trying to talk myself into anything and that's when the Holy Spirit did what it does.
As an aside, I want to make sure that when I wrote about upbringing above, I don't want to dismiss people who grew up in a Christian family as only being Christian because their family is. I know too many people who were brought up in Christian homes who made their own conscious decision to embrace faith for themselves, and usually after a period of wrestling or wandering. So I hope people didn't read it that way.