Paul’s “big but” now reaches a climax (vv.27-31). “Apart from the Law” yet “conforming the Law.” That where he ends up. Remember, Paul’s concern here is with the people of God, not the individual (v/29). The Gentiles qua Gentiles are not God’s people. Nor are the Jews qua Jews God’s people (see Romans 4). No, God’s intention has always been the Jews would spread God’s blessings to everyone so that ultimately Jew and Gentile together (everyone) will be one people living with God in fellowship and communion.
Ethnic boasting is nullified (v.27). The “law of faith” (v.28) is the operative dynamic in belonging to God’s people. The Law given to the Jews is not an ethnic boundary marker but rather a prescription for the life of those who are God’s people, not a way to become God’s people. And the Jews were to be the means by which everyone else becomes a part of God’s people by faith. God is the God of the Gentiles as well as the Jews, after all (v.29)!
And this is precisely the Law’s intent! It is designed to shape a people whose life together will draw those outside to their God by faith (Deuteronomy 4:5-8). This is the way the Jews “confirm” the Law. Its intent was to call people to faith in Israel’s God, not to be a way of becoming God’s people by keeping its standards. The Law is the way of life of God’s people, not the entrance requirements of joining that people. The Law itself points to the grace of Israel’s God as the way one joins God’s people (Exodus 20:1-2).
And this sets the stage for Paul’s introduction of Abraham into his argument.