John Chrysostom

"Ye know the proof of him, that as a child serveth a father, so he served with me in furtherance of the Gospel." And that I speak not at random, "ye yourselves," he says, "know, that as a child serveth a father, so he served with me in furtherance of the Gospel." He presents then Timothy to them, and with reason, that he might enjoy much honor from them. …

Homily on Philippians 9 ↗

Theophylact of Ohrid

You yourselves, he says, are witnesses that he served me as a son serves a father, not only in bodily needs, but, what is far more important, in the preaching of the Gospel. Therefore, as my son, he is worthy of honor, and as a servant of God — all the more so. Through this he commends Timothy to them, not so much bestowing honor on him as doing good for them; for if they heed him as one most worthy, then from his word they will, of course, receive benefit and be deemed worthy of the highest reward.

Commentary on Philippians ↗

Thomas Aquinas

And if you would know how he has behaved in regard to me, I answer that, Timothy's worth you know, how as a son with a father he has served with me in the gospel, i.e., as though he were a special son: "I sent to you Timothy, my beloved and faithful child in the Lord" (1 Cor. 4:17).

Commentary on Philippians ↗