With the greatest respect to previous posters, Judaism is not the religion of the ancient Hebrews or Israelites of the Old Testament. You are confusing Judaism with Hebrewism, they are not one and the same religion. Hebrewism was the religion of Abraham, Isaac and Jacob and the ancient Israelites of the Old Testament. It was the true religion of Yahwey God. Judaism, which was known as Pharasaism in the days of Jesus Christ, was the religion that was brought back from Babylon by the returning exiles of the house of Judah under Ezra and Nehemiah. It did not, therefore, exist in Palestine at the time of the ancient Hebrews and Israelites of the Old Testament:
"This is not an uncommon impression and one finds it sometimes among Jews as well as Christians - that Judaism is the religion of the Hebrew Bible. It is, of course, a fallacious impression... Judaism is not the religion of the Bible." (Rabbi Ben Zion Bokser, “Judaism and the Christian Predicament”, page 59)
"The return from Babylon and the introduction of the Babylonian Talmud mark the end of Hebrewism and the beginning of Judaism." (Rabbi Stephen F. Wise, formerly the Chief Rabbi of the United States)
"Judaism is, specifically, the religion of a Jewish community living among Gentile peoples and is to be distinguished from the religion of ancient Israel." (Standard Encyclopedia, Vol. 14)
The religion of Hebrewism was based on the Torah (Old Testament), ie God's law. The religion of Judaism is based on the Talmud, known as the "oral tradition" or the "tradition of men" in the days of Jesus. The Talmud, not God's law as set out in the Torah, is supreme as far as most, some would say all, Jews are concerned:
“The Talmud is to this day the circulating heart's blood of the Jewish religion. Whatever laws, customs or ceremonies we observe - whether we are Orthodox, Conservative, Reform or merely spasmodic sentimentalists - we follow the Talmud. It is our common law.” (Herman Wouk, “The Talmud: Heart's Blood Of The Jewish Faith”, New York Herald-Tribune, November 1959)
The fact that Judaism is not the same as Hebrewism, ie that the Jews had replaced God's Law (the Torah) with the oral tradition (the Talmud), is confirmed by the words of Jesus Christ as recorded in the Gospel of Mark:
“Howbeit in vain do they worship me, teaching for doctrines the commandments of men. For laying aside the commandment of God, ye hold the tradition of men” (Mark 7:7-8)
Jesus detested Judaism (Pharisaism). Christianity did not come out of Judaism, it came out of Hebrewism, the true religion of Jesus Christ and the ancient Hebrews and Israelites of the Old Testament.
Sorry, one last quote:
"... you will notice the great difference between the Jewish and Christian religions ... We consider the two religions so different that one excludes the other ... there is no such thing as a Judeo-Christian religion." (Rabbi Moshe M. Maggal, President, National Jewish Information Service, letter of 21 August 1961)