After the new Christian sect fell out of favor with mainstream Judaism (around A. 90) and were driven away, the Jews took the Hebrew version of the Old Testament as their text because the Christians were adept at using the seven “other” books to convert people.
This essay will look at the trifecta of the Church’s authority: The Bible, Tradition and the Magisterium.
Paul tells us in Acts when he addresses the people in Aramaic, he states that he was educated “at the feet of Gamaliel” which is quite significant because Gamaliel was a master of the oral law/tradition.
There was no such thing, of course of anyone having his/her own copy of the bible to look things up.
As for Sacred Tradition (not tradition w/small “t”), it is another way of handing on the faith—the Latin, “Traditio” means “to hand on”.
Almost all of Paul’s letters were composed before any of the gospels were written.
The Magisterium is the interpreter of both Sacred Scripture and Sacred Tradition just as the U. Supreme Court is the guardian and interpreter of the Constitution.