Mission theologians generally are in agreement that mission is not simply a task of the church but THE task of the church. This is not because we have been commanded or commissioned to do this task--although, of course, we have--but because God is a missionary God. God is the one who carries out the divine mandate. This is because God's very character is also missionary. God reaches out to his creation constantly.
The missionary task of the church finds its meaning in the missionary nature of God. The God we encounter in the Bible is not on some sort of divine ego trip, demanding loyalty from a recalcitrant creation but one who draws humanity back to himself for humanity's own good. This is the God we see in Jesus Christ.
Jesus Christ demonstrates the nature of true divinity (Philippians 2:5-8) and by extension true humanity (Genesis 1:26-28). The task of the Church is to reflect that missionary character of God. God, in community reaching out to the world. The divine love overflowing the intratrinitarian nature to the world, as if the love the Trinity has for each other is too great to be contained within the Trinitarian life! That is a crazy statement to make--but true.
The missionary task of the church is to reflect that divine life, in fact that truly human life--that is made in that divine image. The love of the church for each other overflowing to the world in witness and service. This make integral mission not some much a task the church must do but a task that the church cannot not do.
So God's mission is to be God. The church's mission is to be the church.