What is the origin of the Bible and who are Judeo-Christians? Why were some Christians of Jewish origin?
The Old Testament is the core of Israelite/Jewish Scriptures. As Christians we see that Jesus is the fulfilment of those scriptures. He is the God of Abraham, Isaac, and Jacob made flesh. Because of that most early Christians were in fact Jewish who believed that Jesus was the Messiah. God began to expand the preaching of the Gospel to non-Jews (Gentiles) shortly after Jesus rose and a lot through using people like Paul.
The Old Testament is made up of narrative history written between Moses (or Job perhaps) and Malachi. We don’t know a whole lot of how certain books came to be regarded as holy scriptures and some others didn’t. We know a lot more about the process of forming the New Testament in that the Gospels, Acts, epistles (letters), and Revelation were written by people we know of who knew Jesus and were disseminated and agreed upon as holy by a large diverse group of people who either knew Jesus first or second hand.
Judeo-Christians are the amalgamation of culture and people that flow from these two movements. Jew & Christian. It’s mostly just a categorization term that can be very broadly applied.