Abraham believed God, and it was accounted to him for righteousness; that is, God justified Abraham because he believed in His Promise (Gen. 15.1-6).

Abraham’s faith in the Word of the Most High, which could be seen in his obedience, justified him before God. the Lord did not accept Abraham because of his merits, but because of his faith, which led him to deny himself and do all that God commanded without hesitating.

This is what Paul wanted all Jews to understand. If Abraham himself, their father according to the flesh, was justified through faith before the Law had been established, it would be no different with them, much less with the Gentiles.