And that the Gentiles might glorify God for his mercy; as it is written, For this cause I will confess to thee among the Gentiles, and sing unto thy name. And that the Gentiles might glorify God for his mercy - As the Jews were to glorify God for his truth, so the Gentiles were to glorify God for his mercy. The Jews received the blessings of the Gospel by right of promise, which promise God had most punctually and circumstantially fulfilled. The Gentiles had received the same Gospel as an effect of God's mere mercy, having no right in consequence of any promise or engagement made with any of their ancestors, though they were originally included in the covenant made with Abraham; and the prophets had repeatedly declared that they should be made equal partakers of those blessings with the Jews themselves; as the apostle proceeds to prove.
I will confess to thee among the Gentiles - This quotation is taken from Psalms 18:49, and shows that the Gentiles had a right to glorify God for his mercy to them; and we shall see the strength of this saying farther, when we consider a maxim of the Jews delivered in Megillah, fol. 14: "From the time that the children of Israel entered into the promised land, no Gentile had any right to sing a hymn of praise to God. But after that the Israelites were led into captivity, then the Gentiles began to have a right to glorify God." Thus the Jews themselves confess that the Gentiles have a right to glorify God; and this on account of being made partakers of his grace and mercy. And if, says Schoettgen, we have a right to glorify God, then it follows that our worship must be pleasing to him; and if it be pleasing to him, then it follows that this worship must be good, otherwise God could not be pleased with it.
Dr. Taylor gives a good paraphrase of this and the three following verses: As you Jews glorify God for his truth, so the Gentiles have a right to join with you in glorifying God for his mercy. And you have Scripture authority for admitting them to such fellowship; for instance, David says, Psalms 18:49, Therefore will I give thanks unto thee, O Lord, among the Gentiles, and sing praises unto thy name. And again, Moses himself says, Deuteronomy 32:43, Rejoice, O ye Gentiles, with his people. And again, it is evident, from Psalms 117:1, Psalms 117:2, that praise to God is not to be confined to the Jews only, but that all people, as they all share in his goodness, should also join in thanks to their common benefactor: O praise the Lord, all ye nations, (Gentiles), praise him all ye people; for his merciful kindness is great towards us; and the truth of the Lord endureth for ever. Again the Prophet Isaiah expressly and clearly declares, Isaiah 11:10, There shall be a root of Jesse, (that is, the Messiah), and he shall rise to reign over the Gentiles, and in him shall the Gentiles hope: ελπιουσιν· And thus the apostle proves, both to the Jews and to the Gentiles, who were probably unwilling to join with each other in religious fellowship, that they had both an equal right to glorify God, being equally interested in his mercy, goodness, and truth; and that, from the evidence of the above scriptures, the Gentiles had as much right to hope in Christ, for the full enjoyment of his kingdom, as the Jews had: and, taking occasion from the last word hope, ελπιουσιν, which we improperly translate trust, he pours out his heart in the following affectionate prayer.