It is good to teach, if he who speaks also acts. For he who shall both "do and teach, the same shall be great in the kingdom." Our Lord and God, Jesus Christ, the Son of the living God, first did and then taught, as Luke testifies, "whose praise is in the Gospel through all the Churches."
And who is this brother? Some indeed say, Luke, because of the history which he wrote, but some, Barnabas; for he calls the unwritten preaching also Gospel. And for what cause does he not mention their names; whilst he both makes Titus known by name, and praises him for his cooperation in the Gospel, (seeing that he was so useful that by reason of his absence even Paul could do nothing great and noble; for, "because I found not Titus my brother, I had no relief for my spirit,") and for his love towards them, (for, saith he, "his inward affection is more abundant towards you;") and for his zeal in this matter ("for," he saith, "of his own accord he went")? But these he neither equally commends, nor mentions by name? What then is one to say? Perhaps they did not know them; wherefore he does not dwell upon their praises because as yet they had had no experience of them, but only says so much as was sufficient for their commendation unto them (i.e. the Corinthians,) and to their escaping all evil suspicion. However, let us see on what score he eulogizes this man himself also. On what score then does he eulogize? First, praising him from his preaching; that he not only preached, but also as he ought, and with the befitting earnestness. For he said not, 'he preaches and proclaims the Gospel,' but, "whose praise is in the Gospel." And that he may not seem to flatter him, he brings not one or two or three men, but whole Churches to testify to him, saying, "through all the churches."
Some understand this to mean Luke, on account of the Gospel written by him; others, Barnabas, since the apostle calls even unwritten preaching "the gospel." He does not expand in praises of him as he does of Titus, because he was not known to the Corinthians, whereas Titus was well known to them. Nevertheless, he weaves sufficient praise for him as well; for he does not simply say that he preaches the Gospel, but that he is "praised," not in two or three, but in all the churches.
Then when he says, "With him we are sending the brother," he treats of the second minister. In regard to this he does two things. First, he commends him; secondly, he gives the reason why he is sending such earnest messengers (v. 20).
This brother, according to some, is Luke, and according to others, Barnabas. Whoever it is, he recommends him on three points, namely, on his reputation, because of his fame, that is, Luke's, is in the gospel written by him among all the churches, because it was approved by the apostles. Or whose fame, namely, Barnabas', is in the preaching of the gospel among all the churches, because he preached to Jews and Gentiles. Hence it is said of Barnabas in Acts (4:38), that he was a good man, full of faith and the Holy Spirit. He also commends him on his companionship, because "not only that," i.e., not only is he famous, "but he has been appointed by the churches to travel with us in this gracious work," i.e., of my preaching, for which we traveled as pilgrims over the world: "We know that while we are at home in the body we are away from the Lord" (2 Cor. 5:6). And this is true of Luke, because he was one of the seventy-two disciples and a companion of Paul. It is also true of Barnabas, because it was said by the Holy Spirit in Acts (13:2): "Set apart for me Barnabas and Saul for the work to which I have called them." And he was made a companion for this gracious work, namely, to collect the alms, or for this gracious work of preaching, of which it says in Eph. (3:8): "To me, though I am the very least of all the saints." He also commends him from his office, because he is a minister of grace "which we are carrying on": "This is how one should regard us, as servants of Christ" (1 Cor. 4:1); "Who has made us competent to be ministers of a new covenant" (2 Cor. 3:6). But that grace is administered "for the glory of the Lord," namely, that our Lord be glorified by the alms collected after the conversion of many people by our preaching, because, as it says in Prov. (14:28): "In a multitude of people is the glory of a king." Likewise it is administered in order that our will be fulfilled, because we want this to be done; hence, he says, "and to show our good will," i.e., predestined by God, who from eternity predestined us to have such a will.
[AD 108] Ignatius of Antioch on 2 Corinthians 8:18