What does Psalm 57:9 mean?

David vows to praise the Lord in the presence of others. This is in response to David's deep faith, trusting that God will rescue him from his current danger (Psalm 57:1–4). He resolves to proclaim God among "peoples" and "nations." This combination of terms suggests David is thinking of the world beyond Israel. The word translated "nations," especially, is often used as a reference to non-Jewish cultures: the Gentiles.

The complete fulfillment of this praise awaits the reign of Christ over all the earth. Quoting from the Old Testament (Psalm 18:49; 2 Samuel 22:50), Romans 15:9 echoes David's vow and observes how Jews and Gentiles were partly united by faith after the resurrection of Christ. The same passage also looks forward to the perfect uniting of saved Jews and Gentiles in the millennial kingdom in songs of praise to Jesus, the Lamb of God. Verse 10 quotes from Isaiah and says, "Rejoice, O Gentiles, with his people" (cf. Isaiah 66:10). Verse 11 quotes, "Praise the Lord, all you Gentiles, and let all the peoples extol him" (cf. Psalm 117:1). Referring to Isaiah, Romans 15:12 anticipates Jesus' rule over the Gentiles saying, "The root of Jesse will come, even he who arises to rule the Gentiles; in him will the Gentiles hope" (cf. Isaiah 11:10). At that time, a great multitude of redeemed people will praise the Lord God Almighty (Revelation 19:6–8).