I propose that of all of Paul’s writings, the letter to the Ephesians is one that is closest to the letter to the Romans. While granted Ephesians is much shorter, I believe that they both have a similar genre and intention of writing.
Paul makes a point in Romans 9:4 that it is the Israelites who received the adoption as sons and this motif is continued and repeated in Ephesians 1:5 where he says that He predestined us (Israel) to be adopted as his sons.
It’s clear that Paul talks to two groups in Romans: Jews and Gentiles, speaking to them within the framework of individually belonging to Christ and then bringing them together as one people group under Christ. In doing so Paul rebukes their national pride and disunity and calls them to live as one under the one authority, that being God. Within the framework of Romans 13, he makes the distinction that not only did the Jewish law came from God, but also the Gentile’s rules stemming from their authorities and rulers also came from God as he allowed those rulers to rule in the first place. There he triumphantly brings them together as one, saying now you both live as one under God within the framework of the Kingdom of God brought forth via the Holy Spirit through Christ.
We see this unifying thought also happening in Ephesians. Paul makes the claim that it was to Israel whom the promise of adoption as sons came, and then says to the Gentiles: “But you also were included when you heard the word of truth.”
I strongly suspect today that if the Apostle Paul was speaking in a modern context, he would not be saying Jew / Gentile and exhorting them to be one; rather he would be writing his exhortations to the Muslim / Jews / Gentiles to pull their heads in and become one in Christ.