Sing to the Lord, all the earth!
Tell of his salvation from day to day.
Declare his glory among the nations,
his marvelous works among all the peoples!
1 Chronicles 16:23-24
This is a verse from a song of praise that King David wrote for the occassion of bringing the ark of the covenant to its new place in Jerusalem. There he appointed Asaph and his brothers with special duties in watching over it and leading the nation in the worship of the Lord. This was done not only to bring Israel into worship, but also to declare God's greatness among the nations.
David's hope is that all the earth would know the Lord as Israel testified day after day of His salvation. By bringing the worship of God to the capital city of an emerging power in Jerusalem, David set the ark of the covenant front and center on his priority list and the world stage as other nations came to Jerusalem.
David's hope is still why we worship. Christians, too, want the nations to know God in Christ and to tell of His greatness. We want His great salvation, accomplished on the cross and secured forever in the resurrection, to be known to all people. That is why the gospel is at the center of Christian worship, so that those who visit us may see salvation in baptism, in the Lord's Table, and in our gospel worship and preaching. We worship so that the world may know.