What does Acts 21:40 mean?

When the tribune allows Paul to speak to his attackers, he doesn't realize he and Paul are at cross purposes. The tribune—an officer of the Roman cohort in Jerusalem—wants to know why the formerly peaceful temple courtyard turned into a group beating with Paul as its target. He's already asked the attackers but can't get a straight answer (Acts 21:34). When Paul asks to speak—and verifies he is not an Egyptian revolutionary (Acts 21:38–39)—the tribune hopes Paul will say something useful.

Paul knows why he was arrested. Ostensibly, he's being attacked because Jews from modern-day Turkey saw him in town with Trophimus, a Gentile also from that province. Those men also saw Paul in the temple and think Paul brought Trophimus into the temple. Deeper than that, he knows that legalistic Jewish Christians, who have been giving him grief since just after his first missionary voyage (Acts 15:1–2), spread the rumor that he's been teaching Jews they don't need to be circumcised (Acts 21:20–21, 28).

Even deeper than that, Paul knows the mob attacked him because it is God's plan. The Holy Spirit has been telling him—and others—for months that he will find "imprisonment and afflictions" in Jerusalem (Acts 20:22–23; 21:4, 9–11). Since arrest by the Romans is inevitable and his public ministry will be paused, he wants to take this last chance not to defend himself but to give the testimony of how Jesus of Nazareth has changed his life (Acts 22:3–21).

The audience listens until Paul reaches the point where Jesus commissions him to share His message with Gentiles. The mob suddenly remembers why they're angry and shouts at the tribune to take him away. The tribune hasn't learned anything of value—possibly because Paul is speaking the "Hebrew dialect" of Aramaic. He orders Paul flogged—a traditional Roman method of extracting information—which Paul avoids by pointing out he's a Roman citizen (Acts 22:22–29). Paul spends the next five years under house arrest, but he does finally get to Rome.