John Calvin on Acts 17:12

12. And many believed. This is not referred unto the sentence next going before, as if those of whom he spake began to believe, making choice of some of them: for that were an absurd thing. But Luke’s meaning is, because many were added by their example, the Church was increased in that city. And hitherto hath Luke declared the first beginning of the church of Thessalonica, lest any man should think that Paul’s labors did perish through his sudden and violent departure; for unless I be much deceived, he showeth for this purpose what fruit his preaching brought forth in the other city, before he came to the exile of Berea.