Sing unto God, ye kingdoms of the earth - That is - that acknowledge the true God - celebrate his praise. The psalmist sees the conversion of the world to God to be so certain an event that he calls on all nations to join in the song.

Sing unto God - All the inhabitants of the earth are invited to sing unto God, to acknowledge him as their God, and give him the praise due to his name.

Sing unto God, ye kingdoms of the earth,.... Not only the Egyptian and Ethiopian kingdoms, but all the kingdoms of the world; which will now be converted to Christ, and become his, even all the Papal, Pagan, and Mahometan kingdoms; see Revelation 11:15. These are called upon to sing songs and hymns of praise to Christ, who is God, for redemption by him, and salvation in him; and for their deliverance from all the darkness and delusions under which they formerly were;
O sing praises unto the Lord; the Lord of all, the Lord of lords, the Head of the church, and Saviour of the body; and whom those converted nations will acknowledge to be their Lord and King; and make their homage, and bring their tribute of praise to him, for breaking the antichristian yokes that were upon them, and freeing them from the tyranny and bondage with which they were oppressed: this will be fulfilled in the latter day; see Revelation 11:1.
Selah; on this word; see Gill on Psalm 3:2.

God is to be admired and adored with reverence and godly fear, by all that attend in his holy places. The God of Israel gives strength and power unto his people. Through Christ strengthening us we can do all things, not otherwise; therefore he must have the glory of all we do, with our humble thanks for enabling us to do it, and for accepting the work of his hands in us.

To Him who is presented as riding in triumph through His ancient heavens and proclaiming His presence--to Him who, in nature, and still more in the wonders of His spiritual government, out of His holy place (Psalm 43:3), is terrible, who rules His Church, and, by His Church, rules the world in righteousness--let all nations and kingdoms give honor and power and dominion evermore.