4-rational reasons as you know are not lacking

I keep hearing this. What I haven't ever heard is exactly what those rational reasons are. Can you supply some that don't refer to the Bible as a source? As far as I can tell, there isn't any other point for this whole conversation.

What are your rational reasons for belief in an entity that can alter natural laws at will without anyone who isn't a believer ever having seen it? How do you explain the logic of the claim that someone was born of a virgin, was a god in man form, washed away your sins (what's that mean, anyway?), and died and came back to life?

I know it probably sounds like I'm trying to get in your face, but I really am curious how intelligent people can believe all this stuff. I like a good debate with people who have different viewpoints than mine, but this debate keeps stopping at the point where Christians say, "It's not irrational" and atheists saying, "Why do you say that?" and the Christians simply not having an answer. Do you have one?