Setting the Scene a little
In Romans Paul is not rehearsing his gospel teaching to 21st century Anglo-Saxons or to a 16th century Roman Catholic hierarchy. If he had been addressing either of these he would have framed his gospel presentation differently.
In Romans he is addressing a community of Jews and Gentiles that had placed its faith in Jesus as the promised Messiah and King, the promised Savior of the world.
Though he is addressing believers in Jesus he is saying things about all Jews and Gentiles as they relate to God (or not) and to one another in terms of Jesus whom Paul claims is the revelation of God and His saving righteousness.
Paul is speaking to Christian Jews who are part of a nation that God had chosen as His peculiar people, a nation to whom He made promises and a people to whom He gave circumcision in their flesh as a constant reminder of that covenant which He made with them in their father Abraham. He is speaking to members of a nation which God chose out from among all other nations, a nation with whom God made covenants from which He excluded all other nations (Ephesians 2:11-12 and Leviticus 18:1-5). God gave that nation a covenant law (the Sinai covenant) that identified the nation, shaped and guided their lives under His sovereignty and it contained within it public ceremonies that bore witness to God’s redeeming actions worked exclusively among and for Israel (Passover, Weeks and Tabernacles for example). Paul was speaking to members of a nation to which the OT prophets promised a coming redeemer, the Messiah—their Messiah [see Romans 9:1-5]. All this being true it shouldn’t surprise us that his message in Romans is shaped as it is.
It is because the above is true that the gospel Paul and others preached was difficult for many Jews to believe, especially when Gentiles were being blessed and many pious and virtuous Jews who lived by the Torah (but rejected Jesus) were excluded. Paul knew his gospel was offensive to the Jews and in Romans he attempts to explain the way in which his gospel was true and in keeping with God’s faithfulness in working out his purposes with both Jews and Gentiles in mind. [See Romans 15:8-9.]
Americans, a coming “George Washington”
Suppose God had made a covenant with George Washington and his new national children—the Americans—a covenant from which he excluded all other nations. Suppose the Americans had the sign of that covenant in their flesh and a constitution that had the will of God for their lives; a constitution that had public ceremonies that celebrated God’s delivering them from slavery and setting them on the road for ultimate deliverance and blessing which he would bring to them in a coming “George Washington”.
Suppose that promised one came and died and nothing particular had changed. Suppose then a little group of Americans began to say that the coming one had risen from the dead and was now Lord of All and that he was offering the American hope [spoken of in their constitution] to the Chinese, the Russians, the Iranians, the Cubans, the Koreans, the Venezuelans and all the other nations independent of the Americans and independent of the American constitution.
Suppose this group said that many Americans were not going to be blessed with the blessings brought by the new “George Washington” and that those who would be blessed would be blessed independent of the American constitution that had shaped the chosen American nation. Constitutional changes would be made that home-born Americans would have to embrace if they were to share in the blessings under this coming “George Washington” and that the established and traditional constitution no longer had to be adhered to by “newcomers” (foreigners).
And suppose the non-Americans now regarded as equal citizens with the home-born Americans began to be arrogant and look down on the home-born Americans as and claimed that God wanted nothing more to do with the bulk of them (see Romans 11:13-24; 15:27).
That’s something like the setting in which Paul writes his Romans and it is something like the scandalous nature of the gospel he has been preaching and will develop in Romans.
(However misleading the word “constitution” in this setting might be please endure it for illustration purposes.)