Charles Ellicott Commentary Romans 15:9

"and that the Gentiles might glorify God for his mercy; as it is written, Therefore will I give praise unto thee among the Gentiles, And sing unto thy name." — Romans 15:9 (ASV)

For his mercy.—This means on account of His mercy. The Jews had their covenant to appeal to, and the attribute of God most clearly made evident to them in Christianity was His veracity in fulfilling the promises contained in this covenant. The Gentiles had no such covenant, and their admission to the blessings of Christianity was an act of pure grace and mercy, which they could only thankfully recognize. The Apostle then proceeds to quote from the Old Testament a series of passages relating to this ultimate reception and triumph of the Gentiles.

For this cause...—Psalms 18:0, from which this quotation is taken, is attributed by its heading to David himself—a view most commentators rightly believe—as a review of his past life and a thanksgiving for his deliverance from his enemies. David is here understood as a type of Christ. He is said to confess to God among the Gentiles, since He is the head of the Gentile Church, in whose name its praises are offered and by whom they are presented.

Confess...—Compare the note on Romans 14:11. Here the meaning, praise, is more distinctly shown. The confession or acknowledgment of mercies is itself an act of praise.