Acts 13:9 - Coke's Commentary on the Holy Bible

Saul, (who also is called Paul,)— The reasons which have been assigned for Saul's taking the name of Paul, are various and many. Some think that he had the name of Paul given him from converting Sergius Paulus, as Scipio was called Africanus from his conquering Africa, and as other Romans had names given them from subduing other countries. Others suppose that he had received at his circumcision the two names of Paul and Saul; that is, Paul as his Roman name, for he was born a freeman of Rome;—and Saul, as his Jewish name; for he was a Jew, and even an Hebrew of the Hebrews. As therefore he used to be called Saul, while he continued among the Jews, that being a more common and acceptable name among them; so henceforth, being to go among the Gentiles, he took the name of Paul, as one which would be better known, and more acceptable to them. For the same reason Silas, who was afterwards St. Paul's great companion, appears to have had also the name of Sylvanus, and to have gone by the former name among the Jews, and by the latter among the Romans; for he seems to have been a freeman of Rome, as well as St. Paul. Beza thinks, that St.Paul having conversed hitherto chiefly with Jews and Syrians, to whom the name of Saul was familiar, and now coming among Greeks and Romans, they would naturally pronounce his name Paul; 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; and he thinks that the family of this proconsul might be the first who addressed or spoke to him by the name of Paul.