Initially, Judaism was a spiritual walk, based upon the Tanakh—most will know it as the Old Testament Hebrew Scriptures. The first answer above is answered so, because the Angel of the LORD spoken of often in the Tanakh, becomes Jesus Christ or Yeshua Messiah of the New Testament. How that occurred is a long story, and so there isn’t time or room to deal with that right here. There was a grievous problem that occurred around the time that Nebuchadnezzar the King of Babylon at her most wonderful period, took the two last tribes [Judah & Benjamin] in the South of the Country, captive. This captivity lasted for seventy years, which is basically two generations, with the change happening in this manner:
Because the Temple had been taken apart by the armies of the King of Babylon, and the Sanctuary sacked, the people were really downhearted. The prophets Jeremiah, Ezekiel and Zechariah were alive and being used of God together with Daniel, who, from inside Babylon, was also writing prophetic material, but the priests had long gone with the downfall of the Northern Ten Tribes, and during the Babylonian Captivity, the rabbis began to compile the thoughts of the rabbis in regards to certain sections of the Tanakh, and because of the paganism within Babylon, there was much teaching interspersed with philosophic humanism begun there, these saved as works worthy of note, and after the Tribes left Babylon, after the letter of Artaxerxes was given to Ezra the priest giving Royal permission for the rebuilding of the City of Jerusalem, this was begun under both Ezra and Nehemiah.
Throughout this time, Judaism changed greatly, and whereas Tanakh was considered that which should be in practice, the Torah/Law [first five Books of Moses] was basically put away, and the Babylonian Talmud became the study of the religionists of the day. Today, the Talmud, with other writings which have to do with how all things should be done [Mishnah, Gemara] takes precedent over Tanakh, and therefore when Jesus of Nazareth was born in the area of Palestine, His ministry had mostly the charge of a Reformer, Who was trying to bring His people back to a proper understanding of Tanakh, calling all else “the traditions of men,” and making a clear distinction between them, and the Sacred Scriptures that were given to the prophets by the Spirit of Christ.
Because His Kingdom was not of this world, and His Way was one of love—firstly to God, and then to man—even to enemies! this kind of living was antipodal to the core desires of the religionists, whose desires were clearly shown in their calling for Barabbas, who was basically an insurrectionist who loved money and power and fighting even unto the death, and therefore the Jews chose Barabbas as their Messiah, rather than Jesus, for they wanted a man who would bring the people together, so they could fight and remove the Roman yoke from off their necks—not Someone Who spoke of living by love and becoming more interested in spirituality rather than aggressive political endeavors. Today the Jews still look for a coming redeemer, whereas most are ready to be now led captive to a false messiah, for the True Messiah has come and gone, and they failed of receiving Him, that according to the prophecy of Daniel 9: 24–27. This people are still a very aggressive people, desiring only to be the head and not the tail.