John Calvin Commentary Acts 17:12

"Many of them therefore believed; also of the Greek women of honorable estate, and of men, not a few." — Acts 17:12 (ASV)

And many believed. This does not refer to the immediately preceding sentence, as if those of whom he spoke began to believe, with only some of them being chosen; for that would be an absurd thing. Instead, Luke’s meaning is that the Church increased in that city because many were added by their example.

And up to this point, Luke has declared the initial establishment of the church of Thessalonica, so that no one should think that Paul’s labors perished through his sudden and violent departure. For unless I am greatly mistaken, he shows for this purpose what fruit his preaching produced in that city, before he came to his exile at Berea.