Anyone who has ever visited an atheist discussion forum will know that there are plenty of atheists and “freethinkers” who take it as a given that Jesus didn’t really exist, that he is a composite figure created from a patchwork of earlier mythology, and so on. If you ask a professional historian whether Jesus existed, however, you will never receive an answer other than “yes”.
Given that history is all about probabilities, how can historians be so certain? The answer lies in a simple fact that casts all serious doubt aside: the crucifixion. There was nothing that more automatically disqualified someone from consideration as God’s appointed savior than being tortured and executed by the foreign overlords who were ruling over his people and their land. It is simply unimaginable that someone would start with the idea of the Messiah and then, in attempting to invent one from scratch, would come up with the crucified Jesus.
This is not to say that we do not have serious uncertainties about what precisely Jesus said and did, or that we are not sure beyond reasonable doubt that he did not say and do certain things attributed to him in the Gospels, or that the possibility is not a real one that his earliest followers either miunderstood or deliberately miscontrued him in places. But it is to say that, in historical study, where certainty is all but impossible, this is a delightful instance where something is as certain as one could ever hope for. To deny Jesus’ existence would be to deny certainty about everything in the past.
Fundamentalist Christians are ready to assume that Jesus said and did everything the Gospels said he did (even, as Ned Flanders famously said on an episode of The Simpsons, “the stuff that contradicts the other stuff”). Atheist fundamentalists are happy to dismiss his existence altogether. The mainstream of serious historical investigation, as well as of faith, recognizes that our knowledge of the past cannot be obtained in such leaps. Each piece of evidence must be examined on its own merits, and whereas ‘picking and choosing’ what to believe from the Gospels on the basis of personal preference is questionable from most standpoints, recognizing that historians will inevitably be persuaded by the evidence for some things and against others is crucial to any attempt to treat the Gospels and other early Christian sources seriously from a historical standpoint.