Acts 17:9

Taken security] The immediate departure of Paul and Silas renders it probable that Jason gave security that St. Paul would leave the city, and that the Apostle assented to this undertaking, and was thus prevented from revisiting the Thessalonians: see 1 Thessalonians 2:18.

The Epistles to the Thessalonians, who are represented as mainly a Gentile Church (1 Thessalonians 1:9; 1 Thessalonians 2:14), imply a much longer residence at Thessalonica than three weeks. Acts 17:2, therefore, must be understood to mean that he worked for three weeks among the Jews, and afterwards turned to the Gentiles, among whom he laboured for three or four months.