Romans 15:7-13 Glorifying God Together.
Therefore, concerning receiving each other, seeking to edify each other and not sitting in judgment on each other on doubtful matters, Paul says to do so because “Christ also received us, to the glory of God.” (v. 7 Cf. 5:2; 14:1, 3) Of course, Christ received us as sinners and reconciled us while His enemies, and forgave us (Cf. Rom. 5:10; Col. 1:21-22). The glory of God in both cases is the goal-Jew and Gentile alike (vv. 8-9). Chronologically this was the order of His ministry (Mt. 15:24; Acts 3:25-26). Christ confirms the promises to the fathers. Christ did this via the new covenant (9:4-5 Cf. Mt. 26:26-30; Lk. 22:14-23). “For all the promises of God in Him are Yes, and in Him Amen, to the glory of God through us.” (II Cor. 1:20)
Christ also fulfills the promise to the Gentiles (v. 9 Cf. II Sam. 22:50; Ps. 18:49). The promises are to all the children of promise, the children of faith (4:16). As was Paul’s practice, he gives multiple witnesses for the inclusion of the Gentiles and the promise to all. His first quote goes to the last of the old covenantal administrations in David (v. 9). It can also be found in the law with Moses’ song of witness (v. 10; Dt. 32:43), and again from the Psalms (v. 11; 117:1), and the prophet Isaiah (v. 12; Is. 11:1, 10). When God thus fulfills His covenant promises to His people there is hope and “joy and peace in believing.” (v. 13 Cf. 12:12). This is by the power of the Holy Spirit. It is a Trinitarian work.