Albert Barnes on Acts 15:23

And wrote letters. Greek, Having written. He does not mean that they wrote more than one epistle.

By them. Greek, By their hand.

After this manner. Greek, These things.

Send greeting. A word of salutation, expressing their desire of the happiness (χαιρειν) of the persons addressed. Comp. Mt 26:49; Mt 27:29, Lk 1:28, Jn 19:3.

In Antioch. Where the difficulty first arose.

And Syria. Antioch was the capital of Syria, and it is probable that the dispute was not confined to the capital.

And Cilicia. Acts 6:9. Cilicia was adjacent to Syria. Paul and Barnabas had travelled through it; and it is probable that the same difficulty would exist there which had disturbed the churches in Syria.