The Rabbi Saul from Tarsus, having had his moment of Divine clarity handed to him in spades, did NOT ‘invent’ Christianity, nor did he ‘hijack’ that belief.
Before that moment, he was the zealot pursuer accuser of Christians, which means he had foreknowledge of their beliefs, activities, and demeanor, i.e., “he was previously exposed to it”.
His moment ‘on the road’, brought to mind, all that he had witnessed, and made it ‘his to own’, as we say, today.
Therefore, with his knowledge of the Talmud, the Ta’anach, the Torah, he was Divinely directed to bring those teachings that reinforce, and more deeply expound, ‘the teachings of the Master’. (ref: ‘I am but a slave’).
His ‘letters’ go to churches of future linkpins, in Revelations. His ‘letters’ go to those churches, that have formed from the local Pagan/Roman communities, and have had no ‘direct exposure to Jesus’, as well.
(How would YOU manage, were you to be set as a ‘remote office of one’, with no manuals or corporate directives, and only the ‘breakroom information brokers’ knowledge, to go on? No data systems, just a pen, ink, and paper, with an occasional speaking arrangement? And, as time went by, the DHS is after your head.)
Talmud, as I understand it, did not exist until a few centuries after Paul’s life.
Saul/Paul was *not* a Jewish rabbi. His teaching was not of Judaism. He was a Hellenist.