What does Acts 17:2 mean?

Paul, Silas, and Timothy are in Thessalonica on the northwest coast of the Aegean Sea in Macedonia. When Paul comes to a new city, he typically first preaches at a synagogue (Acts 13:5; 14:1; 18:4). Because Jesus is the Jewish Messiah and Christianity is a natural progression of Judaism, the Jews and devout Gentiles in the synagogue will have the historical context to understand who Jesus is and what He came to do. Synagogues also have a tradition of inviting well-educated visitors to speak at their weekly meetings. Paul is as qualified as any Jew would wish to be (Philippians 3:4–5).

We only have a handful of Paul's messages in the book of Acts. Although he tailors his message to his audience, it's reasonable to expect his messages in synagogues are similar. Paul's message before the synagogue in Thessalonica shows how the Jewish Scriptures prophesy that the Messiah must die and rise again (Acts 17:3). Likely, he repeats much of the speech he gave to the Pisidian Antiochenes (Acts 13:16–41). There, he showed how David's assurance that God would not let His Holy One see corruption (Psalm 16:10) meant the Holy One would die but rise again. This, he implied, did not apply to David but to the Messiah—much like Peter reasoned in Acts 2:25–32.

After Thessalonica and Berea, Paul will use quotes from Greek poets to explain to Athenian philosophers how the Creator God calls for repentance (Acts 17:22–31). Before Felix, he sneaks in the gospel with his legal defense (Acts 24:10–21). In front of Agrippa and Bernice, who know Judaism, he gives a detailed witness of Jesus' work in his life (Acts 26).