Lesslie Newbigin in The Gospel in a Pluralist Society says that "Mission begins with a kind of explosion of joy." Missional expansion is driven by gospel exultation. This is what exultation is: The explosion of joy resulting from the seeing of Jesus in the hearing of the gospel. So Paul's Damascus road experience is there between the lines of his missionary journeys. The early church's rapid expansion a direct result of awe coming upon every soul (Acts 2:43). Wherever we see Christ capturing a heart, we see a body that can't help but run and tell. So Isaiah's availability to the hardest of mission fields is fueled by his exultational joy in the beatific vision of Christ (John 12:41) and the gospel word of atonement.
John Piper, in his now-classic work on global missions, Let the Nations Be Glad, famously wrote, "Mission exists because worship does not." The idea is that the church is on mission to create disciples of Christ, increasing the numbers of worshipers of Christ in places where he is not worshiped, so that more and more of the earth will be full of worship, that God's name would be praised greatly. God's vision for the earth (Habakkuk 2:14) is the missiological vision. Piper is right. Mission does exist because worship does not. At the same time, however, mission exists because worship does. Real worshipers are missionaries. Or they are impostors (as Spurgeon says). Indeed, not only does worship drive mission, mission is itself an act of worship.