“…in order that the Gentiles might glorify God for his mercy.” (Romans 15:9)
How does Paul unpack the word “glorify” from verse 9? He does it with four Old Testament quotations in verses 9–12.
As it is written, “Therefore I will praise you among the Gentiles, and sing to your name.”
And again it is said, “Rejoice, O Gentiles, with his people.”
And again, “Praise the Lord, all you Gentiles, and let all the peoples extol him.”
And again Isaiah says, “The root of Jesse will come, even he who arises to rule the Gentiles; in him will the Gentiles hope.”
Praise, sing, rejoice, praise, extol, hope.
Glorifying God for his mercy starts with the emotions of joy (verse 10) and hope (verse 12) in the God of mercy. Joy as you savor the merciful God now, and hope as you happily expect to savor him even more in the future. Then that joy and hope overflow in praise (verse 9, 11) and song (verse 9).
This is the essence of gospel worship: Heartfelt, hope-filled joy in the God of mercy overflowing in fitting outward expressions. The reason I say this is the essence of worship is because I know there are other emotions that are part of worship besides joy. Like the sorrows of confession. But these sorrows are not true worship, unless, at root, they are sorrows for our failures to experience joy in the God of mercy. Therefore, joy in the God of mercy remains the essence of gospel worship. And that is really good news, because in God’s design, we get the mercy, God gets the glory. We get the joy, God gets the praise. We revel in hope, God receives the honor. When we call the nations to worship the true God in Christ, that is what we call them to.
—John Piper, “Gospel Worship: Holy Ambition for All the Peoples to Praise Christ”