John Chrysostom

"That no man should glory." That he may excite in us proper feeling touching this gift of grace. "What then?" saith a man, "Hath He Himself hindered our being justified by works?" By no means. But no one, he saith, is justified by works, in order that the grace and loving-kindness of God may be shown. He did not reject us as having works, but as abandoned of works He hath saved us by grace; so that no man henceforth may have whereof to boast. …

Homily on Ephesians 4 ↗

Theophylact of Ohrid

This does not mean that God rejected us who have works, but rather that even those who would have perished with their works, He saved by grace, so that after this no one has the right to boast. For the word "so that" (ίνα) expresses not the cause, but the consequence of the matter.

Commentary on Ephesians ↗

Thomas Aquinas

The second error he rejects is that anyone can believe that faith is given by God to us on the merit of our preceding actions. To exclude this he adds "Not of" preceding "works" that we merited at one time to be saved; for this is the grace, as was mentioned above, and according to Romans 11:6: "If by grace, it is not now by works; otherwise grace is no more grace." He follows with the reason why God saves man by faith without any preceding merits, "that no man may glory" in himself but refer all the glory to God. …

Commentary on Ephesians ↗