"Teaching and preaching the word of the Lord." They did not simply tarry in Antioch, but taught. What did they "teach," and what "preach" (evangelize)? They both (taught) those that were already believers, and (evangelized) those that were not yet such.
Paul and Barnabas stayed in Antioch. In those days, what the apostle Paul said was fulfilled: When Cephas came to Antioch, I opposed him to his face (Galatians 2).
[AD 407] John Chrysostom on Acts 15:35