John Chrysostom

"As they ministered to the Lord, and fasted, the Holy Ghost said, Separate Me Barnabas and Saul for the work whereunto I have called them." What means, "Ministering?" Preaching. "Separate for Me," it says, "Barnabas and Saul." What means, "Separate for Me?" For the work, for the Apostleship. See again by what persons he is ordained. By Lucius the Cyrenean and Manaen, or rather, by the Spirit. The less the persons, the more palpable the grace. He is ordained henceforth to Apostleship, so as to preach with authority.

Homily on Acts 27 ↗

Theophylact of Ohrid

What does "when they served" mean? It means "preached." And the expression "for the work" is used instead of "for apostleship." By whom is Paul ordained? By Lucius and Manaen, or rather by the Holy Spirit. He is ordained so that he might preach with authority. How then does Paul himself say: "chosen not by men nor through man" (Gal. 1:1)? This is in the sense that no man called him and converted him.

Commentary on Acts ↗

Oecumenius

"Set apart for me for the work." That is, to a mission. By whom, then, is he ordained? By Lucius and Manaen, but more by the Spirit. He is ordained so as to preach with authority.

Commentary on Acts ↗

Bede

The Holy Spirit said: Set apart for me Barnabas and Paul for the work to which I have called them. This seems to have happened after the death of Herod, who died in the third year of the reign of Claudius, which, according to the chronicles, is the thirteenth year after the passion of the Lord. …

Retractions on Acts ↗