Albert Barnes Commentary Romans 15:11

"And again, Praise the Lord, all ye Gentiles; And let all the peoples praise him." — Romans 15:11 (ASV)

And again. (Psalms 117:1). The purpose of this quotation is the same as before. The apostle accumulates quotations to show that this was the common language of the Old Testament, and that he was not depending on a single expression for the truth of his doctrine.

All you Gentiles. In the psalm, it is all you nations; but the original term is the same.

And laud him. Praise him. The psalm is directly relevant. It is a call on all nations to praise God—the very point in the apostle's discussion.