What would you say to a trinitarian who believes and advocates that Rabbinical Judaism teaches the Trinity? (See the thread titled Did Christians “invent” the Trinity?-2)
I've never heard such a claim because rabbinical Judaism is descended from the Pharisees who rejected Christ.
I'm not a Jewish theologian and can't speak at length to what they believe, but the RCC makes much of Jewish doctrine. The Jerusalem Bible, approved by the RCC, does not attribute the writing of the Pentateuch to Moses, but to different scholarly traditions, eg. "Elohists," "Yahwists," etc., that supposedly wrote during different time periods.
I had one book written by a Jewish Scholar who made the claim that the Jews invented monotheism, in the books introduction. I didn't bother reading past the introduction as it seemed that the author was a "fool."
One thing I am confident of regarding Jewish theology is that the Pharisees believed in a resurrection while the Sadducees didn't, and that they awaited the return of Elijah before the coming of the Messiah to sit upon the throne of David. Modern synagogues still keep an ornate and unoccupied chair in an isolated spot called Elijah's chair, symbolic of his expected return. However, there is nothing specifically in the belief of modern Judaism (to my limited knowledge) that anticipates "the messiah" to be the Son of God and equal to God.
At least one contemporary Jewish sect believed that their rabbi was the Messiah and expected him to rise from the grave when he died, but they did not consider him to be more than a man with the anointing of God upon him.
I can't speak to what the 1st century Jews believed beyond what scripture and the writings of Josephus say, but its clear that even then their beliefs were not uniform.