I was raised in faith (in Greece, which at the time was an overwhelming 97% Eastern Orthodox), and this faith survived all the questioning and rebellion of early adulthood. It's as simple as that. I have wavered in many things, but those are aspects of religious practice, not faith itself. My belief that God exists remains unshaken, despite having been through the gamut of crises that life doles out to anyone who has managed to reach middle age.
To me, belief in God means belief that there is more to this world than I can perceive, in space or time; that existence ultimately makes sense, even if I can't understand it; that I need to treat everyone and everything around me with the respect and love they deserve, for the only reason of being parts of this existence as much as I am. That I do matter in this world, although it does not revolve around me.