How does the life of Abraham affirm the inclusion of uncircumcised Gentile Christians in God’s covenant?

The Gentile Christians in Rome could possibly have thought that David’s beatitude in Psalm 32:1–2, which Paul had just quoted in Matthew 4:6–8, applies only to those who, like him, lived under the law and was circumcised. Is the forgiveness of sins not perhaps only for them? Paul emphatically rejects such a restrictive reading. He now combines David’s words with those spoken to Abraham and clarifies that the beatitude of David, who was under the law and was circumcised, also applies to people who are outside the law and uncircumcised, such as Abraham, who lived prior to the introduction of the law and circumcision. Circumcision was introduced only towards the end of Abraham’s life, and served as a seal upon the justification by faith which he had already received even as an uncircumcised person. That is why, even as Gentile Christians, we can call Abraham our father. He is the father of both the circumcised and the uncircumcised. The mystery of Romans 4:1 is solved in Romans 4:9–12. Since faith precedes circumcision and the law, believing Gentile Christians in Rome cannot be considered as outsiders, even if they are not members of the synagogue. They are heirs of our father Abraham along with all the believers from among the Jews. Therefore, they do not have to feel like they are second-class citizens compared to the old, estimable Jewish people of God who lived under the law.¹