John Chrysostom

"Only Luke is with me." For he adhered to him inseparably. It was he who wrote the Gospel, and the General Acts; he was devoted to labors, and to learning, and a man of fortitude. "Take Mark, and bring him with thee, for he is profitable to me for the ministry." It is not for his own relief, but for the ministry of the Gospel that he wanted him. For though imprisoned, he did not cease to preach.

Homily on 2 Timothy 10 ↗

Theophylact of Ohrid

He was constantly at his side, wrote the Gospel and the Acts of the Apostles. The apostle speaks of him in another epistle: "the brother, whose praise is in the gospel throughout all the churches" (2 Cor. 8:18). He demands him not for his own comfort, but for the service of the Gospel. For even in chains he did not cease to preach. …

Commentary on 2 Timothy ↗

Thomas Aquinas

"Only Luke is with me." He retained him for preaching the Gospel, in which he was most gracious: "whose praise is in the Gospel through all the churches" (2 Cor 8:18). Then when he says, "take Mark and bring him with you," he assigns him a companion. This Mark was also called John and was a cousin of Barnabas. In Acts it is recorded that Barnabas would have taken with him John also that was surnamed Mark (Acts 15:37); but Paul vetoed it. …

Commentary on 2 Timothy ↗