What does Acts 22:21 mean?

Paul is in the court of the temple, at the steps of the Antonia Fortress—the Roman army barracks. Jews from modern-day western Turkey accused him of bringing a Gentile into the temple and tried to kill him (Acts 21:27–40). Paul hadn't brought his Gentile friend into the temple, but he did walk around Jerusalem with him. Paul tries to use his conversion experience to explain why (Acts 22:1–20).

Here, he is talking about his return to Jerusalem after he decided to follow Christ. He was praying at the temple when Jesus told him to leave the city; the Jews there would rather kill him than listen to his message. Paul was confused—surely the Jews would see that if he joined the church after persecuting it, Jesus must be the Messiah (Acts 22:17–20). But Jesus said, no. He needed to leave. His ministry would be to the Gentiles, not the Jews in Jerusalem.

Jesus was right: the Jews tried to kill Paul (Acts 9:29). Back in Jerusalem decades later, they are trying again. The mob has listened so far, but when Paul brings up the Gentiles, they return to their raging and demand the Roman tribune arrest him (Acts 22:22). This is all in God's plan; the Holy Spirit has been telling Paul he will be arrested (Acts 20:22–23). The next three years aren't pleasant, but the arrest does get Paul to Rome.