May the God of endurance and encouragement grant you to live in such harmony with one another, in accord with Christ Jesus, that together you may with one voice glorify the God and Father of our Lord Jesus Christ. Therefore welcome one another as Christ has welcomed you, for the glory of God.
For I tell you that Christ became a servant to the circumcised to show God’s truthfulness, in order to confirm the promises given to the patriarchs, and in order that the Gentiles might glorify God for his mercy. As it is written,
“Therefore I will praise you among the Gentiles,
and sing to Your name.”
And again it is said,
“Rejoice, O Gentiles, with His people.”
“Praise the Lord, all you Gentiles,
and let all the peoples extol Him.”
And again Isaiah says,
“The root of Jesse will come,
even He who arises to rule the Gentiles;
in Him will the Gentiles hope.” (Romans 15:5-12)
The theological point is the bringing of the Gentiles under God’s mercy, so they can share together with Jews in the hope that is in Christ, as the final quote in the catena declares, “The root of Jesse shall come, and He who rises to rule the Gentiles. In Him the Gentiles shall hope”(Rom. 15:12; cf. Is. 11:10). But the choice of Paul to use worship texts is more than a matter of finding useful texts regarding the Gentiles. It places the proper outworking of the passage in the actual united worship of the Roman believers.
—John W. Taylor, “The Lord’s Supper in Romans: The Common Meal and United Worship in Romans 14–15 as Demonstration of the Gospel,” 12