What does Acts 17:9 mean?
Paul is used to the general sequence of events he experiences in Thessalonica. He starts by teaching in a synagogue, showing the truths of the Messiah hidden in Jewish prophecy and how Jesus of Nazareth fits those prophecies (Acts 9:20; 13:16–41; 14:1; 17:1, 10; 18:4; 19:8). He watches as some of the Jews and many of the Gentile God-fearers believe Jesus' story and accept salvation. When the Jews who refuse to believe get jealous and start to cause problems, Paul leaves the synagogue and finds another place for the new church to meet. Inevitably, those Jews will rile up the people of the city who have nothing to do with the synagogue. Paul will then either quietly escape (Acts 14:5–6) or suffer persecution, such as being stoned and left for dead (Acts 14:19) or being beaten and imprisoned (Acts 16:22–24).This is the first recorded time that Paul escapes quietly (Acts 17:10) while his recent converts suffer persecution. The unbelieving Jews of the synagogue have taken "some wicked men of the rabble" (Acts 17:5) and pulled Jason, who is apparently hosting Paul and his team, out of his home. Fortunately, the mob takes Jason and some of the others of the church to the authorities (Acts 17:6–7). The new converts apparently escape serious physical attack.
The antagonistic Jews are not finished, however. Paul and Silas will make their way southwest to Berea. The people of the synagogue will react to their message in an admirable way: they will thoroughly compare Paul's words with Jewish Scriptures to see if he's right. But the Jews from Thessalonica, like those of Pisidian Antioch and Iconium (Acts 14:19), will follow and continue their quest to drive Paul out of Macedonia. Paul will flee to Athens and won't meet up with Silas and Timothy again until he reaches Corinth (Acts 17:10–15).
"Security" is a bond that Jason would forfeit if Paul or the church caused any more trouble. It's to the credit of the leadership of Thessalonica that they handled the disturbance with so little drama. Although Paul had to leave, no one seems to have been physically attacked. Still, Paul saw this situation as direct action of Satan as it set up a situation where Paul couldn't return as quickly as he wanted (1 Thessalonians 2:18). In fact, he didn't return until his third major missions trip (Acts 20:1).
Acts 17:1–9 relates that Paul, Silas, and Timothy traveled to Thessalonica, having left Luke in Philippi. As usual, they start in the synagogue, showing how the prophecies of the Jewish Scriptures say the Messiah must die and rise from the dead. And as usual some of the Jews and many of the Gentiles believe them, while other Jews reject their message. For the first time, however, Paul's antagonists can't find him or his team, so they attack several converts. The new church protects Paul, Silas, and Timothy and sends them southwest to Berea.
Acts 17 describes how Paul's ministry travels down the coast of Greece. In Thessalonica, some Jews and God-fearing Gentiles believe while other Jews start a riot (Acts 17:1–9). The Bereans study the veracity of Paul's statements—until the Thessalonian Jews arrive and threaten to start another riot (Acts 17:10–15). Paul flees to Athens where the Epicurean and Stoic philosophers accept Paul's argument when he uses Greek poets to introduce God as the creator of the world, but lose interest when he mentions the resurrection from the dead (Acts 17:16–34).