Notes on the Bible, by Albert Barnes, , at sacred-texts.com
The occasion and the author of this psalm are alike unknown. DeWette regards it as a temple-psalm, and agrees with Rosenmuller in the supposition that it was sung either at the beginning or the end of the service in the temple. Knapp supposes that it was used as an intermediate service, sung during the progress of the general service to vary the devotion, and to awaken a new interest in the service, either sung by a choir or by the whole people.
In many manuscripts of Kennicott and De Rossi, and in several editions of the Scriptures, this psalm is united with the following. The psalm has no independent character or meaning of its own, and seems to have been designed, like the "Doxologies" in our Books of Psalms and Hymns, to be attached to other psalms as occasion might require. There is no psalm designed for public worship to which it might not thus properly be attached.
O praise the Lord, all ye nations - The idea is that God has a claim to universal worship, and that all the nations of the earth are under obligations to adore him as the true God. He is not the God of the Hebrew people only, but of all people; his praise should be celebrated not merely by one nation, but by all. This is one of the passages in the Old Testament, anticipating what is more fully disclosed in the New Testament, in which the sacred writer extends his vision beyond the narrow boundaries of Judea, and looks to the world, the whole world, as the theater on which the true religion was to be displayed, and for which it was designed. It is language such as would be indited by the Spirit of inspiration on the supposition that the time would come when the barrier between Jews and Gentiles would be broken down, and when all the nations of the earth would be in the possession of the true religion, and would unite in the worship of the same God. This doctrine, however, was not fully made known until the coming of the Redeemer. The announcement of this was made by the Redeemer himself (compare Mat 8:11; Mat 12:21; Mat 28:19); it was the occasion of no small part of the trouble which the Apostle Paul had with his countrymen (compare Act 13:46; Act 18:6; Act 21:21; Act 22:21; Act 26:20, Act 26:23); it was one of the doctrines which Paul especially endeavored to establish, as a great truth of Christianity, that all the barriers between the nations were to be broken down, and the Gospel proclaimed to all people alike, Rom 3:29; Rom 9:24, Rom 9:30; Rom 11:11; Rom 15:9-11, Rom 15:16, Rom 15:18; Gal 2:2; Eph 2:11-18; Eph 3:1-9. It is under the gospel that this language becomes especially appropriate.
Praise him, all ye people - People of all lands. The word here rendered "praise" - שׁבח shâbach - means properly to soothe, to still, to restrain - as, for example, billows Psa 89:9; and then, to praise, as if to soothe with praises - mulcere laudibus, Pacuv. The idea of soothing or mitigating, however, is not necessarily in the word, but it may be understood in the general sense of praise. We may in fact often soothe or appease people - angry, jealous, suspicious people - by skillful flattery or praise - for there are few, even when under the influence of anger or hatred, who may not thus be approached, or who do not value praise and commendation more than they do the indulgence of passion; but we cannot hope thus to appease the anger of God. We approach him to utter our deep sense of his goodness, and our veneration for his character; we do not expect to turn him from anger to love - to make him forget his justice or our sins - by soothing flattery.
For his merciful kindness is great toward us - His kindness; his compassion; his love. All nations - all people - may say this, and therefore the psalm is adapted to universal praise. Especially may this be said in view of the love of God to mankind in the gift of a Saviour - a Saviour not for any one people especially or exclusively, but for the world, Joh 3:16.
And the truth of the Lord endureth for ever - All that God has said: his declarations; his promises; his assurances of mercy. They are the same in all lands where they are made known, and they are the same in all ages of the world. Truth is a representation of things as they are; and truth, therefore, must be ever the same. What was true in the first ages of the world in regard to the relation of the sum of the squares on the two sides of a right-angled triangle to the square of the hypothenuse is true now, and will always be true; and so, what God has affirmed at any one time will always remain the same in all ages and in all lands. What was truth to Abraham is truth to us; what was truth to Paul is truth to us; what was truth to the martyrs is truth to us; what is truth to us will be truth to all generations of the world in all lands, and will be truth forever. This fact, too, is a just foundation for universal praise, and therefore the psalm is so adapted to be used in all lands and among all people. How often in our own language has this psalm been the medium of the utterances of praise in Christian sanctuaries:
"From all that dwell below the skies,
Let the Creator's praise arise;
Let the Redeemer's name be sung,
Through every land, by every tongue.
Eternal are thy mercies, Lord;
Eternal truth attends thy word;
Thy praise shall sound from shore to shore,
Till suns shall rise and set no more.