Missions is not the ultimate goal of the church. Worship is. Missions exists because worship doesn’t. Worship is ultimate, not missions, because God is ultimate, not man. When this age is over, and the countless millions of the redeemed fall on their faces before the throne of God, missions will be no more. It is a temporary necessity. But worship abibes forever (Romans 12:1-2).

—John Piper
Let the Nations Be Glad: The Supremacy of God in Missions

Related: Passage for January from the 2008 Desiring God Calendar.