Not a side work, optional, or elective
Missions is inherent in the very nature of Christianity and is a true product of our personal faith in proper relationship to a Spirit-enlightened understanding of biblical Christianity. Such a statement does not mean that missions need not be taught and nurtured in the Christian church or that it grows spontaneously or automatically.
Nothing is spontaneous in Christianity. All must be cultivated and nurtured. But it does mean that when the whole counsel of God is taught, believed and obeyed, missions will cease to be considered a side work or something we may engage in or not.
It will cease to be optional and “elective.” It will not be merely a work of the church, beneficial and praiseworthy; it will be the work of the church, absolutely essential to the church to retain her Christian character and purpose. It will become primary and dominant in the purpose and activity of the church, with all powers geared toward accomplishing the task.
George W. Peters, A Biblical Theology of Missions (Chicago, IL: Moody Press, 1972), 349.