Were Abraham, Isaac, Jacob and Moses Jews? The vast majority of people
believe that this is true and educated Jewish people will tell you that
this is true. But does that actually make it true? The primary
confusion here is the confusion between Judaism, the religion,
and the descendants of Judah.
Abraham was the father of Isaac. Isaac was the father of Jacob, who was later called Israel. Jacob or Israel had twelve sons: Reuben, Simeon, Levi, Judah, Dan, Naphtali, Gad, Asher, Issachar, Zebulun, Joseph and Benjamin. Each of these sons of Jacob, with the exception of Joseph, had families which grew large enough to become tribes.
One of these tribes was the tribe of Judah who came to be referred to as Jews, just as the Levites were named after his brother Levi.
King David descended from the tribe of Judah and therefore was a Jew. Not that it matters, but I descended from Judah. According to my genealogy, he is my 84th Great Grandfather on my father's side.
Abraham, Isaac and Jacob spoke the Hebraic language and therefore were considered Hebrews, but they all predated Judah and therefore were not Jews.
And Moses, to whom God gave the tablets of the law, descended from Levi, Judah's older brother, and therefore was not a Jew or descendant of Judah. Now, almost from the moment that Moses came down from the mountain, all of these tribes of Israel, recognized all the laws and statutes God gave to Moses as a religion, which came to be called Judaism.
Just about anyone, of any race, can convert to Judaism, the religion, and call himself a Jew or Jewish, but only a descendant of Jacob's son Judah can be a Jew by blood. In short, every Jew is an Israelite, but not all Israelites are Jews.