In the psalms some translations do not always render the plural of the Hebrew word am (people) as peoples. Yet the psalms maintain a significant distinction between the singular and plural of the word. When it appears in the singular, it refers to Israel, the people of God. When it occurs in the plural, it refers to the other nations and is a synonym for the Gentiles. The only exceptions to this are an occasional singular that is qualified by another word or phrase, as in Psalm 114:1: When Israel went out of Egypt, The house of Jacob from a people of strange tongue… The word “people” there is clearly a reference to Egypt but is qualified by of a strange tongue.
This is important in Psalm 47and especially so in verse 9, which should read, The princes of the peoples have gathered together, the people of the God of Abraham. The ESV, NIV, RSV and ASV all have “peoples” or “nations,” but the KJV, NKJV and NASB have “people.”
The Psalm is about the ascension of our Lord Jesus Christ to the right hand of power. God has gone up with a shout, The LORD with the sound of a trumpet (v. 5). He has become the King of all the earth (v. 7) and reigns over the nations (v. 8).
Therefore, the psalm calls on the peoples (plural) to clap their hands and shout (v. 1) and to sing praises to God (v. 6). He will subdue the peoples under us, And the nations under our feet (v. 3) is probably addressed to Israel in the Old Testament and the church in the New Testament as fighting against, overcoming and ruling over the nations in Christ. Today we achieve that power by the preaching of the gospel (cf. Ps. 149).
The result of this revelation of the power and majesty of Christ our king and God is not in this case the judgment and destruction of the peoples, but their gathering together to become the people (singular!) of the God of Abraham. They will not only be themselves a people of God, but they will inherit the promise made to Abraham when God said, In your seed all the nations of the earth shall be blessed (Gen. 22:18). Gentiles will become children of Abraham (Rom. 4:16–17).
The psalm is rooted in God’s covenant with Abraham and has been fulfilled in the exaltation of Christ to be universal king. These two great facts explain the urgency of the apostle Paul to preach the gospel where it had not before been heard and our participation in the commonwealth of Israel and household of God. The Lord has made of Jew and Gentile one new man (Eph. 2:15). The shields of the earth belong to Christ. He has inherited all peoples, and out of those peoples he effectively calls some to be grafted into the olive tree of Israel (Rom. 11:17).
See a metrical setting of the psalm by clicking this link.