Monotheism, a belief in the absolute unity and singularity of God, is central to Judaism, which regards the worship of a person as a form of idolatry. Therefore, considering Jesus a deity would be forbidden .
What is the Messiah supposed to accomplish? The Bible says that he will:
A. Build the Third Temple (Ezekiel 37:26-28).
B. Gather all Jews back to the Land of Israel (Isaiah 43:5-6).
C. Usher in an era of world peace, and end all hatred, oppression, suffering and disease. As it says: "Nation shall not lift up sword against nation, neither shall man learn war anymore." (Isaiah 2:4)
D. Spread universal knowledge of the God of Israel, which will unite humanity as one. As it says: "God will be King over all the world—on that day, God will be One and His Name will be One" (Zechariah 14:9).
The historical fact is that Jesus fulfilled none of these messianic prophecies.
Christians counter that Jesus will fulfill these in the Second Coming, but Jewish sources show that the Messiah will fulfill the prophecies outright, and no concept of a second coming exists.