John Chrysostom

But these very words are favorable to the Law, and how they are so, shall be hence manifest. Let us attend accurately to his very words. He said not, The Law is loss: but "I counted it loss." But when he spake of gain, he said not, I counted them, but "they were gain." But when he spake of loss he said, "I counted": and this rightly; for the former was naturally so, but the latter became so, from my opinion. "What then? Is it not so?" says he. It is loss for Christ. And how has the law become gain? …

Homily on Philippians 11 ↗

Theophylact of Ohrid

Here the heretics who condemn the law say: behold, Paul calls it "loss" — how then could it have been given by God? But first of all, let us be grateful that the Holy Spirit so arranged it that they accept these words as if speaking in their favor. If this were not so, they would simply have destroyed these words, as they did many others. Then, pay attention: the apostle did not say directly that the law is loss, but "I count" it "as loss," since the law in itself is not loss. …

Commentary on Philippians ↗

Thomas Aquinas

Then when he says, but whatever gain I had, he shows his contempt for the prestige he had under the Law: first, he shows in general why he scorned the things of the Law; secondly, in detail (3:8). He says, therefore: Whatever gain I had, i.e., prestige, namely, to be a Pharisee and so on, I counted as loss for the sake of Christ, i.e., I came to regard them as hindrances. For the observances of the Law, which were effective during the time of the Law, became harmful after Christ; hence he says, loss. …

Commentary on Philippians ↗