What does Acts 9:1 mean?

Saul is a young Jewish man from Tarsus, the capital of the Roman province of Cilicia. He grew up in a predominantly Greco-Roman culture, although he moved to Jerusalem at a fairly young age and trained under the renowned Pharisee Gamaliel (Acts 22:3). In his own words, Saul was a brilliant student, "advancing in Judaism beyond many of my own age among my people, so extremely zealous was I for the traditions of my fathers" (Galatians 1:14). Because of this, he reacted strongly to the teaching that Jesus of Nazareth, whom the Jewish council had executed, was the Jewish Messiah. Saul approved while a mob murdered the Jesus-follower Stephen (Acts 7:58) and started a persecution of the church so fierce most Christians fled Jerusalem (Acts 8:1–3).

Unfortunately for Saul's plan, followers of Jesus took His message with them. One reason Stephen was killed was because he insisted true God-followers needed neither the temple nor Jerusalem to worship Him (Acts 7:1–53). Now, Saul asks for permission to track the Jesus-followers outside Jerusalem to arrest them and bring them back to Jerusalem for trial, where he will vote that they be executed for blasphemy (Acts 26:10). Ironically, his tactics contradict the guidance given by his mentor. Gamaliel had suggested the Sanhedrin ignore the Jesus-followers; if the movement was of God, they wouldn't be able to stop it, and if it wasn't, it would die off naturally (Acts 5:34–39). Saul would rather act.

Saul goes to the high priest because although the entire area is under Roman rule in the civil realm, the Sanhedrin in Jerusalem still has religious authority over those who claim to follow Judaism. The "disciples of the Lord" in this context are not just the Twelve core apostles. They include anyone who follows Jesus. Because of Saul's own persecution, the good news about Jesus has spread even farther north than Damascus to Syrian Antioch (Acts 11:19–20).