John Chrysostom

For the Law requires not only Faith but works also, but grace saves and justifies by Faith. (Eph. ii: 8) You see how he proves that they are under the curse who cleave to the Law, because it is impossible to fulfill it; next, how comes Faith to have this justifying power? for to this doctrine he already stood pledged, and now maintains it with great force of argument. …

Homily on Galatians 3 ↗

Theophylact of Ohrid

For the law requires not only faith, but also works. Since the law, by reason of its impossibility of fulfillment, did not justify but subjected to a curse, grace appeared, showing an easy path — faith, through which, being justified, we receive blessing. Thus it has been proven that faith imparted blessing and justification not only before the law, but even more so after it.

Commentary on Galatians ↗

Oecumenius

"The law is not of faith," but from works. And from this it is clear that "the one who does them shall live by them." Therefore salvation in the law is through works, and not through faith.

Commentary on Galatians ↗

Thomas Aquinas

The minor premise is set down at, "But the law is not of faith." First, the minor is set down; Secondly, it is proved (v. 12): "but he that doth those things, shall live in them." He says therefore that "the law is not of faith." But this seems to conflict with the truth that the Law commands one to believe that there is one God, which pertains to faith. Therefore the Law had faith. …

Commentary on Galatians ↗