Acts 13:12 - Joseph Benson’s Commentary on the Old and New Testaments

Then the deputy Or proconsul; when he saw what was done What a wonderful miracle was performed, yielding to such convincing evidence; believed the gospel; being astonished Εκπλησσομενος, being struck with astonishment; at the doctrine of the Lord At the confirmation thus given to it, and probably also at the internal evidence which he soon discovered in it, and which broke in with increasing lustre on his mind. The reader will observe, that at this period of the history, Luke has changed Saul's name, calling him Paul, without assigning any reason for so doing. Some learned men have supposed that this change was made by Saul himself, in honour of the proconsul, who they think was, perhaps, Saul's first convert from among the idolatrous Gentiles, or the first person of high rank of that character who was converted. For it was customary among the Romans to assume the name of a benefactor whom they highly esteemed. Thus the Jewish historian, Josephus, took the name of Flavius, in compliment to Vespasian, with whom he was in high favour. But it is more probable, that, coming now among the Romans and Greeks, they adapted his name to their own language, and so called him Paul instead of Saul; as one whose Hebrew name was Jochanan, would be called by the Greeks and Latins, Johannes; by the French, Jean; by the Dutch, Hans; and by the English, John. Perhaps, however, the family of the proconsul might be the first who addressed, or spoke to him, by this name. But in whatever manner it happened, it is certain that ever after this he was known only by this name; and, being the apostle of the Gentiles, he himself used it as a name most familiar to them. From this time forth, likewise, Paul is generally mentioned by the historian before Barnabas: because, by his success in preaching at Paphos, and by the greatness of his miracles, he was now shown to be the principal person; although, formerly, he was mentioned after Barnabas, because he was a younger disciple, and because his apostolical authority was not fully understood.