Verse 1
O praise the LORD, all ye nations: praise him, all ye people.
Psalms 117:1-2 -Cf. Introduction to Psalms 116:1-19
O praise the Lord, all ye nations - Israel's call to the Gentiles to praise Yahweh for His mercy and His truth displayed to her, as set forth in Psalms 116:1-19 (cf. Psalms 47:1; Psalms 67:1-3; Psalms 98:3-4).
Verse 2
For his merciful kindness is great toward us: and the truth of the LORD endureth for ever. Praise ye the LORD.
For his merciful kindness is great toward us: and the truth of the Lord endureth forever - the two attributes mentioned by Paul in Romans 15:8-12 as those which Jesus Christ came to manifest, so that the Gentiles might "rejoice with His people," the Jews, because of the universal blessing through the latter. 'Jesus Christ was a minister of the circumcision for the truth of God (His faithfulness to His word) to confirm the promises made unto the fathers, and that the Gentiles might glorify God for His mercy.'