Jesus's credibility as the Messiah the Jewish people foresaw is predicated on the fulfillment of certain prophesies set forth in the Old Testament. But the writers of the New Testament seemed content to pick and choose what was needed to be fulfilled, blatantly ignoring some prophesies.
For example: "...they shall beat their swords into plowshares, and their spears into pruning hooks; nation shall not lift up sword against nation, neither shall they learn war anymore." (Micah 4:3)
In other words, the Messiah would rule at a time of world peace. This was clearly not the case in the days of Jesus, and arguably hasn't been the case since then. In fact, the very idea of the Crusades is hypocritical in light of this fact.
But the Crusades may have been necessary in the eyes of the Middle Age Christians, because the Messiah was supposed to usher in a period when everybody in the world worshiped under one God:
"And it shall come to pass that from one new moon to another and from one Sabbath to another, shall all flesh come to worship before Me, says the Lord" (Isaiah 66:23)
This passage is clear in its intent, but seems to be ignored by Christians. Even if you make the supposition that all followers of Islam, Judaism, and Christianity worship the same God, you still have the Hindu as well as other smaller religions who do not, not to mention atheists, agnostics, and Buddhists who do not worship any God.
The Crusaders who spilled the blood of millions in the name of Christ tried to fulfill this prophecy, God love 'em (summarily ignoring the first prophecy mentioned, but they may have felt that was justified given that we've never had a period of world peace since the placement of Jesus as the Messiah anyway...) but failed even trying to force-feed their propaganda to the world at large.
In addition, the Messiah was supposed to be a direct male descendant of King David:
"And when your days [David] are fulfilled, and you shall sleep with your fathers, I will set up your seed after you, who shall issue from your bowels, and I will establish his kingdom. He shall build a house for my name, and I will make firm the throne of his kingdom forever..." (2 Samuel 7:12-13)
Since Jesus was not Joseph's biological son, it follows that he was not a direct descendant of David in the sense given here.
Even though I don't personally believe any of it, I thought it would be interesting to give a Jewish spin on the arguments for and against the Jesus myth, since it's not currently represented here. If you consider these criteria (and there are other criteria that Jesus doesn't fulfill as well, these are really just the most glaring) you really can't accept Jesus as the Messiah.
If you take all this, combined with the facts that
1)there is no historical record of Jesus's time on earth;
2)many elements of the Jesus story come from pagan tradition; and
3)the books of the New Testament were written down long after the events supposedly took place,
you can see how the early Christians cobbled together bits and pieces of Old Testament and pagan lore to form a cult that is really based solely on myth. The bottom line is that Jesus does not fulfill the most important prophesies set forth in the Old Testament in any way, so his credibility as the Messiah predicted by the Jews is non-existent.