Though historians seem to disagree on the matter of whether there is evidence that Jesus actually existed or whether he's just part of a biblical story or allegory, for the sake of argument I will assume that Jesus was a real person who lived about 2000 years ago in Judea and was crucified by Pilate. As with all historical events in the realm of alternate history, the events surrounding the crucifixion could certainly have gone a different way, allowing him to escape Pilate's wrath. Since I know little about the specifics, I can't say with detail exactly how this could happen, but I can surmise as to the consequences. If he isn't martyred, Christianity goes down the crapper, or at least Christianity as we know it, since Christian mythology is founded on the assumption that Jesus was crucified. That also means Islam would be butterflied away, since Jesus was long dead when Islam evolved from Judeo-Christian beliefs. That might leave Judaism as the dominant religion in the western Old World, assuming no other religions or variants on Judaism become more popular. Buddhism and Hinduism would still be around, as they predate Christianity, but with all the butterflies springing forth from a POD nearly 2000 years ago, there could be any number of unrecognizable superstitious belief systems today. We definitely wouldn't be using the Christian calendar; perhaps the Jewish or Buddhist ones would become the standard. I have no idea whether the absence of Christianity and Islam would eventually promote the prevalence of secularism or not, but it's possible that we might have a more secular, progressive society today than in OTL.
I'd like to say "Kudos" to Bill Cameron and Blue Max for speaking up so rationally for secularism (especially in the context of alternate history) earlier in this thread. And for the record, I believe that all religions possess an equal amount of validity.