Why do you believe in God?

I am always troubled when I encounter people (online) who are atheists. It troubles me especially if the person is smart, or very intelligent (and people who consider themselves atheists usually are). It troubles me because it poses to me a very great challenge (and one that is very burdensome, too) -- Please defend your religion!

Agh!

If an atheist would ask me, "Why do you believe in God?" My first answer would probably be, "Because I *know* He exists." Not a very convincing answer for a rationalist, lol.

Then I'd probably say that I don't have all the answers yet (not even the basic answers), that I am just starting on my faith journey, studying my faith, reading up on apologetics and theology. I plan to study all these, little by little, as I go through life. Apologetics and theology are tremendously vast areas of study, and countless really smart and intelligent people are devoting their profession/lives to studying them, and it seems that they can never exhaust the subject; it seems that they can never plumb the depths of God's mystery (Of course, for how can finite beings with limited intellects understand the infinite, the absolute Being?).

What I believe is basically this: We can know God through faith and reason. Reason can point us to God's existence, but it has limits. It is faith which actually helps us to know Him deeply and personally.