John Chrysostom

"Hearing," he says, "of thy love." This is wonderful, and much greater than if being present he had seen it when he was present. For it is plain that from its being excessive it had become manifest, and had reached even to Paul. And yet the distance between Rome and Phrygia was not small. For he seems to have been there from the mention of Archippus. …

Homily on Philemon 2 ↗

Theophylact of Ohrid

Here he praises him for his goodness. From Phrygia it would not have been heard in Rome about his love and faith, if it had not been great. Since you love all the saints, that is, the faithful, you should also love Onesimus, for he too is now a believer — so that through this you may show yourself as one who loves the Lord as well. Do you see what compelling thoughts he gathers in his mind toward the fulfillment of the request?

Commentary on Philemon ↗

Jerome

But if Paul always prayed for the saints and for the better ones (Philemon, who is indeed a saint, who also demonstrated such great faith and love that he was known not only by his reputation, but also by his works) and it is likely that he always prayed for Philemon, so that the faith and love he had in Christ, and in all his holy ones, through the communication of faith and the operation of knowledge, would be kept by the mercy of Christ in all goodness. …

Commentary on Philemon ↗

Thomas Aquinas

Stating the matter of his giving thanks and of his prayer, he shows what he asks when he prays for them. The matter of this was the needs and goods of Philemon, namely, both charity and faith. For without charity nothing avails and through it all things are had. 1 Corinthians 13:1: 'If I should speak with the tongues of men and of angels, but do not have charity, I have become as sounding brass or a tinkling cymbal.' Again, without faith no one can love God, because he does not truly know God. …

Commentary on Philemon ↗