QUESTION : If Jesus is Messiah, why don't the Rabbis believe it?
This is not exactly true, David. Did you know that, by the end of the first century, the Jewish historian, Neander, reported that over a million Jewish people in Israel believed Yeshua, Jesus, to be the Messiah?
Of course, as 'Christian' anti-Semitism kicked in, these numbers dropped, but, since the 19th Century, they've been rising again.
But I will answer your question because it's true to say that the majority of Rabbis don't believe in Jesus.
Firstly, just a reminder about how Jews tend to treat their leaders. Moses was rejected by the majority in the wilderness and David wasn't always Mr Popularity. A constant theme, particularly at the time of Elijah and Isaiah, is of a faithful remnant, indicating that the proportion of 'God's people' would always be low within the Jewish population as a whole. So Jews, in common with the rest of the world, have always found it difficult to accept new ideas, particularly as is seems to go against received wisdom.
Let's face it, if a Rabbi declared Christianity to be true (and many have), then he would immediately be struck off, declared insane or uneducated or both. This is because the study of the Messiahship of Jesus is actively discouraged within the Jewish community. But surely Rabbis can be wrong?
It is up to each person, Rabbi or otherwise, to come to their own conclusion, as long as their search is sincere. If tradition is going to stop you from using your own mind, then you're not as intellectually and spiritually free as you think. Being born a Jew, whether Orthodox or otherwise, shouldn't stop you from thinking for yourself.
But some Rabbis have thought for themselves. For example, early this century Rabbi Isaac Lichtenstein in Hungary public admitted belief in Jesus as Messiah to his congregation, who followed suit.
In conclusion, David, I just say one thing. Pick up a copy of the New Testament and read it. Read the Gospel of Matthew first, then write to me what you think.
Be brave, be honest