John Chrysostom

Further, they were possessed with another apprehension; it was written, "Cursed is every one that continueth not in all things that are written in the book of the Law, to do them." And this he removes, with great skill and prudence, turning their argument against themselves, and showing that those who relinquish the Law are not only not cursed, but blessed; and they who keep it, not only not blessed but cursed. …

Homily on Galatians 3 ↗

Theophylact of Ohrid

Since they were afraid that for not observing the law they would be subjected to a curse (for it is written: cursed is he who does not observe what is written in the law), he shows the complete opposite, namely, that blessed are those who leave the law and come to faith, just as the faithful Abraham received the blessing.

Commentary on Galatians ↗

Oecumenius

"Therefore those who are of faith are blessed." Those who are of faith united to Abraham and are counted as his offspring, not those who are of the flesh.

Commentary on Galatians ↗

Thomas Aquinas

Then when he says, "Therefore, they that are of faith," he draws the conclusion from the premises. Accordingly, the argument can be formulated thus: God the Father announced to Abraham that in his seed all nations would be blessed. But those who seek to be justified by faith are the children of Abraham. Therefore, "they that are of faith," i.e., who seek to be justified through faith, "shall be blessed with faithful," i.e., with believing, "Abraham."

Commentary on Galatians ↗