What does Acts 16:22 mean?

Paul has expelled a fortune-telling demon out of a slave girl, ruining her owners' income source. In response, the owners accuse Paul and Silas of advocating unlawful customs (Acts 16:21). The charge is a serious one. The Roman Empire strongly controlled what gods its inhabitants could worship. Judaism was authorized, but while Rome sometimes grandfathered Christianity under Judaism, Christians teach the worship of a man, Jesus of Nazareth, placing Him on the same level or higher than the emperor. The Roman statesman Cicero, who lived in the first century BC, said in De Legibus, ii.8, "No person shall have any separate gods, or new ones; nor shall he privately worship any strange gods, unless they be publicly allowed." The response of the crowd and the city leaders is immediate, possibly due to the fact Philippi, although in Macedonia, was a Roman city (Acts 16:23–24).

It so happens that the response of the magistrates, itself, was illegal. Paul and Silas were Roman citizens, who were entitled to a trial before being beaten. Though the local leaders attempt to cover up their error, Paul ensures they admit to their mistake (Acts 16:36–39).

Later, Paul will write to the Thessalonians about this day, how he and Silas had "suffered and been shamefully treated at Philippi" (1 Thessalonians 2:2). Despite this and despite the treatment they receive in Thessalonica, Paul says, "our coming to you was not in vain" (1 Thessalonians 2:1). God promised Paul he would suffer for the spread of the gospel (Acts 9:16), and he did (2 Corinthians 11:24–28).

After Philippi, Paul, Silas, and Timothy will go southwest to Thessalonica. Unlike Philippi, which didn't even have a synagogue, Thessalonica had many Jews. Some of the Jews in Thessalonica will be stubborn enough not only to start a riot and drive Paul and Silas away, but also to follow them to Berea and start more problems. It will get so bad, the believers rush Paul away to Athens (Acts 17:4–15).