God's Mercy Is Great Toward Us.

The unsearchable riches of gospel-grace, which are to be the matter or our praise. In the gospel, those celebrated attributes of God, his mercy and his truth, shine most brightly in themselves and most comfortably to us; and the apostle, where he quotes this psalm, takes notice of these as the two great things for which the Gentiles should glorify God (Romans 15:8, 9), for the truth of God and for his mercy. We that enjoy the gospel have reason to praise the Lord, For the power of his mercy: His merciful kindness is great towards us; it is strong (so the word signifies); it is mighty for the pardon of mighty sins (Amos 5:12) and for the working out of a mighty salvation.

For the perpetuity of his truth: The truth of the Lord endures for ever. It was mercy, mere mercy, to the Gentiles, that the gospel was sent among them. It was merciful kindness prevailing towards them above their deserts; and in it the truth of the Lord, of his promise made unto the fathers, endures for ever; for, though the Jews were hardened and expelled, yet the promise took its effect in the believing Gentiles, the spiritual seed of Abraham. God's mercy is the fountain of all our comforts and his truth the foundation of all our hopes, and therefore for both we must praise the Lord. - Matthew Henry