John Chrysostom

"Brethren, be ye imitators of me, and mark them which so walk even as ye have us for an ensample." He had said above, "beware of dogs," from such he had led them away; he brings them near to these whom they ought to imitate. If any one, saith he, wishes to imitate me, if any one wishes to walk the same road, let him take heed to them; though I am not present, ye know the manner of my walk, that is, my conduct in life. …

Homily on Philippians 12 ↗

Theophylact of Ohrid

Above he said: "beware of dogs," and thus distanced the Philippians from them. Now he draws them near to those who lead a good life; for this is what "mark" means, that is, pay attention to them and, seeing in them the original pattern, imitate them; as in me you have an example, so also in them. For he taught them not only by words, but also in his life and conduct he showed himself as an example; and in this consists perfect teaching.

Commentary on Philippians ↗

Thomas Aquinas

Then when he says, join in imitating me, he urges them to imitate him and others, but to avoid the wicked: first, he makes his point; secondly, he gives the reason (3:18). He says, therefore: Because I regard these things as dung, that I may gain Christ, brethren, join in imitating me in this: "The sheep hear his voice" (Jn. 10:3). I am the shepherd; you are my sheep by imitating me: "Be imitators of me, as I am of Christ" (1 Cor. 11:1), and mark, i.e., carefully consider, those who so live as you have an example in us. …

Commentary on Philippians ↗