As Jesus indicated in his final words as recorded in Matthew 28:18-20, his authority over the nations manifests largely in the sending out of his disciples as his witnesses to the nations. He is the Lord, and his disciples his servants who in obedience to his command go out into all the world to preach the gospel to every creature. As narrated therefore in the post-resurrection teaching of Jesus and the birth of the church at Pentecost through the descent of the Spirit and the preaching of the apostles, the church’s mission is not an afterthought to its existence. It is rather the very meaning and purpose of its existence. As the advent of Christ into the world was, as the Creed says, “for us and our salvation”, so also does the church sent by Christ live not for itself but for the world Christ came to save. T.F. Torrance explains:
[I]f the Church does recover the New Testament vision, she will see that the great task of the Church is the redemption of the world, and not a comfortable life in little religious churches and communities. The Church simply cannot keep alive unless her eyes are upon the farthest horizons of the world, unless she keeps herself in line with the master-passion and world-outlook of Christ who was the propitiation not for our sins only but for the sins of the whole world. It is for that reason that mission work does not arise from any arrogance in the Christian Church: mission is its cause and its life. The Church exists by mission, just as fire exists by burning. Where there is no mission, there is no Church. Of course, it is ultimately a secondary question whether we mean by mission Foreign Missions or preaching the gospel at home. Mission, gospel preaching, is the spreading of the fire that Christ cast upon the earth. He who does not propagate this fire shows that he is not burning. He who burns propagates the fire (Brunner). But to burn, the fire must have fuel to burn—that is why it must always be reaching out and out and out.
Jesus Christ came, he said, not to be ministered unto but to minister and to give his life a ransom for many. If the Church claims to follow this Christ, she most learn that she cannot claim to be Christian until her major effort is engaged in ministering to others after the pattern of her Lord. But think of any average church in this country you care—is it not true that the people’s main business is to gather together just in order to be ministered unto, instead of ministering themselves?… Thus the vitality of the Church is sapped by in-breeding, by in-growing. It is a major disaster that the Church has become introvert (i.e., turned in upon itself) when it ought to be extrovert (i.e., turned out toward the world). The Church has become static and self-regarding, instead of an army of conquest.
The major task of the Church in all ages is world mission. If the master-passion of Jesus was the redemption of the world, how is it at all possible for us to call our churches ‘Christian’ whose major purpose is certainly very far different from the passion of Christ? Our major emphasis is upon ourselves—and in so doing we have brought about in the Church a complete reversal of the will and command of Christ; we have betrayed the supreme purpose of the Cross. The Church of today appears simply not to believe that by losing her life for Christ’s sake and the gospel’s, she will find it, that the Church exists only by mission. Instead the Church tries miserably to cultivate her own strength, and becomes self-centred and soft, and impotent over against the ills of the world.
The Church needs to be turned inside out, her whole effort and life must face outwards, and only inwards so far as it is necessary in her effort to evangelize the world. Only if the Church determines to put this first and foremost in her life and work, and in the life and work of every single individual country church, will she begin to have the blessing she craves from God. Instead of trying to cherish a tiny quiver of flame, shielding it from all the draughts and winds that blow, let her fling it out into the storms of the world where it is meant to be, and it will become a raging fire radiating heat and light. If the Church exists by mission, just as fire exists by burning, then the Church at home will never be healthy and strong until she is bent upon consuming the world with the fire of the Cross.
Torrance touches on something here that is of supreme importance both for the church and the world. If indeed it is true that the church exists by mission as a fire exists by burning, then a church without its mission is a dying, if not already dead, church. I have talked with pastors who seem to want their churches to reach a place of “stability” before throwing themselves into the task of mission both locally and globally. Their conception of the church is one in which mission is secondary to the church’s being, as if the church could attain a healthy and mature existence apart from being on mission! However, if Torrance is correct — and I am convinced that he is — then such churches are chasing after wind. The church will never become stable, healthy, or mature unless it renounces its quest for such things as ends in themselves and sacrifices itself for the sake of the world. What Jesus said about carrying the cross applies to churches too! A church that seeks to save its life will lose it, while a church that loses its life for the sake of Christ and his gospel will find it.
This will no doubt require great suffering and sacrifice on the part of the church. Yet this is part and parcel of the church’s calling. “For it has been granted to you that for the sake of Christ you should not only believe in him but also suffer for his sake” (Phil. 3:29). As Torrance puts it, the preaching of the gospel is a casting of fire on the earth. Fire can provide warmth, but it can also cause burns. It can purify, but it can also destroy. To cast fire on the earth is to throw the world into foment and upheaval, and the church which does so will certainly face opposition and persecution. Nevertheless, this is a casting of fire without which the church fizzles out of existence, and it is only in the furnace of mission that it receives its true self.
 T.F. Torrance, Gospel, Church, and Ministry, ed. Jock Stein (Eugene: Pickwick, 2012), 83-84.