Acts 17:9

And when they had taken security of Jason, and of the other, they let them go.

The mob broke into Jason's house to drag Paul and Silas before the authorities, but they were not found, for friends had already sent the apostles out of the city toward Berea. In their disappointment the mob seized Jason with his brother and the other believers and dragged them before the magistrates. Because Paul and Silas were absent and could not be found, Jason was held responsible in their place for having received them.

The charge was driven by Jewish envy at the apostles' success in gaining large congregations, including leading women of the city and multitudes of Gentiles. It was also driven by a plan to regain favor with Rome after a recent Jewish insurrection had left the Jews suspected and restricted in liberty, by appearing as loyal citizens, gratifying malice toward the apostles, and shifting suspicion onto Christians. The magistrates credited the determined accusation that the apostles were disturbing the peace and raising an insurrection by acting contrary to Caesar's decrees in saying there is another king, one Jesus, which was interpreted to mean that Paul taught Christ would come a second time in that generation and reign on earth as king over all nations.

The taking of security means the magistrates released Jason and the others after taking security from them, placing Jason under bonds that bound them to keep the peace. After the release, the threat of further violence led the believers to send Paul and Silas away by night to Berea.