For if Abraham were justified by works, he has something in which to boast; but not before God.
All Commentaries on Romans 4:2 Go To Romans 4
Augustine of Hippo
AD 430
Since Abraham without the law obtained glory not by the works of the law (as if he could fulfill the law in his own strength), since the law had not yet been given, the glory belongs to God, not to him. For he was justified not by his own merit, as if by works, but by the grace of God through faith.