The glory of God — and our joy in him — is the heart of mission.

John Piper writes,

The goal of missions is the gladness of the peoples in the greatness of God. "The LORD reigns, let the earth rejoice; let the many coastlands be glad!" (Psalm 97:1). "Let the peoples praise you, O God; let all the peoples praise you! Let the nations be glad and sing for joy! (Psalm 67:3-4). . . Missions begins and ends in worship.

(Let the Nations Be Glad, 3rd ed. [Grand Rapids: Baker, 2010], 36)

Lesslie Newbigin writes,

There has been a long tradition which sees the mission of the Church primarily as obedience to a command. It has been customary to speak of "the missionary mandate." This way of putting the matter is certainly not without justification, and yet it seems to me that it misses the point. It tends to make mission a burden rather than a joy, to make it part of the law rather than part of the gospel.

If one looks at the New Testament evidence one gets another impression. Mission begins with a kind of explosion of joy. The news that the rejected and crucified Jesus is alive is something that cannot possibly be suppressed. It must be told. Who could be silent about such a fact?

The mission of the Church in the pages of the New Testament is more like a fallout which is not lethal but life-giving. One searches in vain through the letters of St. Paul to find any suggestion that he anywhere lays it on the conscience of his reader that they ought to be active in mission. For himself it is inconceivable that he should keep silent. "Woe to me if I do not preach the gospel!" (1 Corinthians 9:16). But nowhere do we find him telling his readers that they have a duty to do so. . . .

At the heart of mission is thanksgiving and praise. . . . When it is true to its nature, it is so to the end. Mission is an acted out doxology. That is its deepest secret. Its purpose is that God may be glorified.

(The Gospel in a Pluralistic Society, [Grand Rapids: Eerdmans, 1989], 116, 127, emphasis and paragraphing mine)