What does Acts 23:20 mean?

Paul is in the barracks of the Roman army in Jerusalem. While visiting the temple, Jews from modern-day Turkey wrongfully accused him of a crime against both the Mosaic and Roman laws. The Roman tribune took Paul into custody to keep him safe long enough to figure out what is going on (Acts 21:27–33).

Lysias, the tribune, is on his third day of investigating. During the first, he discovered the mob attacking Paul didn't know why they were doing so (Acts 21:33–34). The tribune let Paul speak to the crowd, but learned nothing from it (Acts 21:37—22:22). Back at the barracks, the tribune planned to beat the information out of Paul—until he found out Paul was a Roman citizen (Acts 22:24–29). The next day, the tribune took Paul to the Sanhedrin, the ruling Jewish council, to ask their perspective. All the tribune learned was that Paul can manipulate national religious leaders into a physical altercation (Acts 23:1–10).

The third day, Paul's nephew learns that the Sanhedrin is planning to pretend to bring Paul back so they can make a proper investigation. Normally, the tribune would be relieved; he needs to figure out if he should charge Paul with a crime. But Paul's nephew knows the invitation is a ruse. Forty zealous Jews plan on killing Paul on his way to the meeting (Acts 23:12–16). The young man warns the tribune. As law enforcement, the tribune has to protect Paul anyway, but since Paul is a Roman citizen he is doubly responsible for Paul's safety.

The tribune acts quickly. He swears the boy to secrecy and makes plans to "rescue" Paul by sending him to Caesarea Maritima, to the governor (Acts 23:22–24). He then conveniently forgets to attend the trial (Acts 24:22). Paul stays under house-arrest for two years before finally sailing to Rome (Acts 24:27).