Saint Paul, called Saul before his conversion on the road to Damascus, was a Jew born in Tarsus. Saul belonged to the Pharisee sect and was a loyal Roman citizen who actively persecuted the early Christians in Jerusalem. His persecution of the followers of Jesus was not simply because he was following orders. Saul believed that these new Christians were attacking the foundations of his own faith. His convictions were so strong that he sought and received permission from the High Priest in Jerusalem to capture the Christians in Damascus to bring them to justice in Jerusalem. It was on his way to Damascus that Saul was knocked from his horse by a flash of light from heaven and where he heard Saul, Saul, why are you persecuting me? marking his conversion. (The event of Saint Paul's conversion is celebrated every year on the 25th of January.)
Tradition holds that Paul was bit on the hand by a viper, but the lethal venom had no effect; thus was an outward sign of God's protection over Saint Paul.