Paul asks what advantage the Jew has and answers, "Much in every way! Because first of all, they were entrusted with the revelations of God." If some were without faith, their unbelief does not nullify the faithfulness of God. "May it never be! Yes, let God be found true, but every man a liar."
Are we better than they? No, in no way, for both Jews and Greeks are all under sin. Paul gathers words from the Scriptures: "There is no one righteous; no, not one." No one understands or seeks after God; all have turned aside. The Scriptures go on to describe the harm sin does with words and actions, and that there is no fear of God before their eyes. So every mouth is stopped, and the whole world is accountable to God. "For through the law comes the knowledge of sin."
But now apart from the law, a righteousness of God has been revealed, testified by the law and the prophets. It is through faith in Jesus Christ to all who believe, for there is no distinction. All have sinned and fall short of the glory of God, being justified freely by his grace through the redemption that is in Christ Jesus. God sent him to be an atoning sacrifice through faith in his blood. This demonstrated God's righteousness, so that he might be just and the justifier of him who has faith in Jesus.
Where then is boasting? It is excluded, not by a law of works, but by a law of faith. "We maintain therefore that a man is justified by faith apart from the works of the law." Is God the God of Jews only? He is the God of Gentiles also, since there is one God who will justify both by faith. "Do we then nullify the law through faith? May it never be! No, we establish the law."