When he wasn’t drinking in pubs and shooting billiards, the greatest Scotsman who ever lived, David Hume, took apart human reasoning, piece by piece.  Of particular relevance to the holiday season, in his essay, "Of Miracles," he critiqued one the foundational chestnuts of the Christian tradition.  In order for something to be a miracle, it must be supernatural.  If it's truly supernatural, then it's beyond natural laws.  If it's beyond natural laws, then it's a violation of anything we humans have the capability of understanding or reasoning about -- is, in other words, beyond rationality.  A Christianity without miracles isn't much of a religion, since all of it's basic beliefs become, at best, metaphors for natural phenomena (virgin birth, resurrection, et al. would be just strange ways of talking about more pedestrian subjects that we all know occur under natural laws).  Thus, Christianity isn't rational. At best, it's nonrational (as opposed to merely irrational), the belief being what's called fideistic, which is the act of accepting a proposition (like 'there is a god') without sufficient evidence, or, really, any evidence at all, because of the supposed value in faith itself.  Many Christians don't like this approach, but it's hard to see any other viable alternative.  Of those who bite the bullet and continue to believe, the most famous are:

Blaise Pascal, who argued that one should believe in a god because if there is a god, the possible reward for being right outweighs the possible punishment for being wrong and you don't get jackshit if you're right about there not being one.