Missions is inherit in the nature of Christianity:
There are, then, four words – Commission, Compassion, Community, Continuity – each of them representing at some period of the Church’s life a major element in missionary endeavor. But none of these, nor all of them taken together, can constitute the basic argument. ment. None of them touches the true profundity of this matter. In the last resort, the one reason for missions is Christ. He only is the motive. God’s presence in Him is the only sufficient cause.
The fact is, belief in missions and belief in Christ stand and fall together. To say “I believe that God so loved the world, that in Christ He gave everything He had, gave His very self,” to use such words not lightly or conventionally but in spirit and in truth, means that the one who uses them binds himself irrevocably to make self-giving giving the controlling principle of life; and this is the very essence of missions. To put it otherwise, the concern for world evangelization tion is not something tacked on to a man’s personal Christianity, which he may take or leave as he chooses; it is rooted indefeasibly in the character of the God who has come to us in Christ Jesus. Thus it can never be the province of a few enthusiasts, a sideline or a speciality of those who happen to have a bent that way. It is the distinctive mark of being a Christian. To accept Christ is to enlist under a missionary banner. It is quite impossible to be (in the Pauline phrase) “in Christ” and not participate in Christ’s mission in the world. In fact, here is the surest test whether we have truly grasped what Christ was doing by His life and death and resurrection, tion, or whether we have failed even to begin to understand the Gospel that He brought. James Denney once heard a distinguished missionary say – “Some people do not believe in missions. They have no right to believe in missions: they do not believe in Christ.” That stringent comment is a salutary reminder that a missionary outlook is a direct inevitable deduction from a saving knowledge of Jesus. The sole ground of missionary endeavor is Christ.’
Dr. James S. Stewart quoted in George Peters. A Biblical Theology of Missions (pp. 348-349). Kindle Edition.