Doubtless they bragged that their ancestors went back to Abraham. They claimed him as their father. Not so, said Paul. God counted Abraham a righteous man not because he began to practice circumcision, but because he blazed the trail of faith. Those who respond to God's grace by believing him are the true children of Abraham, heirs to the blessings God promised him.
Faith brings blessing.
Paul made the point abundantly clear. Paul uses the term in different ways at different times. Sometimes he refers to the Decalogue, or the Ten Commandments. At other times, he refers to the Pentateuch, or the first five Books of the Bible. The point is that the law is expansive.