What does Acts 16:23 mean?

A demon-possessed slave girl followed Paul, Silas, Luke, and Timothy to the river where they met to pray. There, she loudly declared, "These men are servants of the Most High God, who proclaim to you the way of salvation" (Acts 16:17). The description suggests she was being intrusive, obnoxious, or possibly sarcastic. The men successfully ignore her for several days. Eventually, Paul decides he's had enough and expels the demon. Unfortunately, the girl's owners depend on the money the fortune-telling demon makes for them. It was not against Roman law to expel a demon, but it was illegal to preach a new religion and encourage the worship of a god not endorsed by the Roman government. The girl's owners charge Paul and Silas with advocating unlawful customs (Acts 16:16–21).

The onlookers join in the persecution, beating Paul and Silas until the magistrates more officially tear off the men's clothes and beat them with rods (Acts 16:22). This proves to be a mistake. Philippi was a Roman city, despite the fact it sits on the border of Macedonia and Greece. That may be why the populace is so riled up about this new religion. But it also means the people knew Roman citizens had special rights. For one, they were entitled to "due process:" they could not be punished, let alone beaten and imprisoned, without a fair trial. While it is true that most of the population in the Roman Empire were not citizens, especially the Jews, Paul and Silas were. They could charge the magistrates with false imprisonment. Instead, they will merely demand an official apology and move on to Berea (Acts 16:35–40).