John Calvin Commentary Acts 13:5

"And when they were at Salamis, they proclaimed the word of God in the synagogues of the Jews: and they had also John as their attendant." — Acts 13:5 (ASV)

He says that they first began to preach the gospel in Salamis, a famous city of Cyprus. Nevertheless, they seem to begin incorrectly; for since they were sent especially to the Gentiles, they preach the word of God, nevertheless, to the Jews. I answer that they were not so exclusively committed to the Gentiles that, setting aside the Jews, they were obliged to go straight to the Gentiles. For when God made them teachers of the Gentiles, He did not depose them from the office which they had previously exercised. Therefore, there was no reason to prevent them from laboring with both Jews and Gentiles. Indeed, furthermore, it was fitting that they should begin with the Jews, as we shall see at the end of the chapter.

Moreover, Luke adds incidentally that they were helped by John. For Luke's meaning is not that John was their servant for personal needs or physical comforts. Rather, in that John was their helper in preaching the gospel, Luke commends his godly zeal and diligence. This was not because their level of honor was equal, but because the labor was common to all. For this reason, John had less excuse afterward when he forsook the holy calling.