John Chrysostom

"For if I build up again those things which I destroyed, I prove myself a transgressor." Observe the Apostle's discernment; his opponents endeavored to show, that he who kept not the Law was a transgressor, but he retorts the argument upon them, and shows that he who did keep the Law was a transgressor, not merely of faith, but of the Law itself. …

Homily on Galatians 2 ↗

Theophylact of Ohrid

Notice his wisdom: they were saying that the one who violates the law is a transgressor, but he, on the contrary, shows that the one who observes it is a transgressor, going not only against the faith, but also against the law itself. For the law itself led me to the faith and persuaded me to leave it. Further on he will point this out, but for now he says that the law has ceased, and we have testified to this by the fact that we destroyed it, having departed from it. …

Commentary on Galatians ↗

Oecumenius

We have nullified the law by allowing it, and have run to Christ. If then we seek to establish it again, we make ourselves transgressors in that we attempt to set up again what was dissolved by us. But observe his sense: those men thought themselves transgressors because they did not keep the law; he shows that they are transgressors because they hold to it. "I consider myself a transgressor." For by once more obeying the law, I show that as a transgressor I first permitted myself, and I believed in Christ.

Commentary on Galatians ↗