Paul's name was originally Saul. He grew up learning both the Jewish law and the Greek ways of discussing things. When the Christian movement began, after the death of Jesus, he was strongly against it. He worked for the Roman Government and led the persecution, (the arrests and killing) of many Christians in Israel and the nearby area.
While he was on the road to Damascus in search of Christians there, he had a vision. In the vision Jesus Christ spoke to him, telling Saul that his persecution of Christians was a persecution of Jesus himself, and that it did not please God. Saul was blinded by the vision. A short time later he met Ananias of Damascus , a disciple of Jesus, and his sight came back to him
Saul was baptised as a Christian. He spent the next three years studying the Jewish scriptures again to find explanations for the Christian teachings.