Acts 18:4 - Joseph Benson’s Commentary on the Old and New Testaments

And he reasoned in the synagogue, &c. The Jews being numerous in Corinth, Paul, according to his custom, began his ministry in the synagogue; and persuaded That is, endeavoured to persuade; the Jews and Greeks It is probable that most of these Greeks, since they attended the Jewish synagogue, were a kind of proselytes. It is possible, however, that some of them might not be such, but Gentiles, who were drawn out of curiosity to attend in the synagogue (though they did not commonly worship there) to hear such an extraordinary preacher as Paul was, especially considering the miracles which he wrought at Corinth, and to which he so often refers in the two epistles afterward written to the church formed there.