According to A. Katherine Grieb (The Story of Romans: A Narrative Defense of God’s Righteousness, p. xxii) Paul makes two essential arguments in Romans:
(1) “…it is the same God who made covenant promises to Israel who is now calling Gentiles into Paul’s congregations…”
(2) “…this does not mean that God has been unfaithful to the people of Israel.”
Following Karl Barth and Wayne Meeks she suggest that these two arguments are important because if God was not faithful to Israel there is no way to know that God will be faithful to those of other nations that he welcomes into the new covenant.
If Grieb is correct how does this influence our reading of various parts of Romans? In part, this seems to be the point of her book which I have begun recently. It will be interesting to see how my reading of Romans might change if I read each section with this theme in mind: God is faithful to his covenant with Israel. He allows the nations to join the covenant. These two realities can be maintained at the same time.