The Relationship Between Judaism and Christianity

[Channalee]

I'm curious why some folks are of the opinion that if Jesus believed himself to be the messiah, if his followers believed him to be the messiah, that such belief, in and of itself, made them apostates.

It's said that in every generation, there is one person born who could possibly be the Messiah. It's not merely the belief in a Messiah that makes one an apostate, else there would have been an awful lot of Jewish apostates in the Lubavitcher community who believed at the time that Rabbi Menachem Mendel Schneerson was the Messiah.  The good Rabbi tried put a stop to it and, when he died and the world hadn't changed, his followers realized that the Rabbi had only been a possible Messiah -- that the time was not yet right for the Messiah to come.
 
The difference with Jesus is that his followers back then and today believe that Jesus rose from the dead, was the son of God, and fulfilled all the requirements to be considered the Messiah.  Christians not only continue to view Jesus as the Messiah, they worship him as being a one-third part of God and/or the son of God.
 
There's also the controversial question put forth by many scholars:  "Did Jesus even exist at all?"  If the story of Jesus was purposely created in order to bring about a social and political change at that time and over the succeeding centuries, it certainly worked.  But I don't think that was quite the change in the world that Judaism's expectations of the Messiah would have fulfilled.