D. Martyn Lloyd-Jones from Unsearchable Riches of Christ: An Exposition of Ephesians 3 (page 253):
The secret of the early Christians, the early Protestants, Puritans and Methodists was that they were taught about the love of Christ, and they became filled with a knowledge of it.
Once a man has the love of Christ in his heart, you need not train him to witness; he will do it. He will know the power, the constraint, the motive; everything is already there. It is a plain lie to suggest that people who regard this knowledge of the love of Christ as the supreme thing are useless, unhealthy mystics.
The servants of God who have most adorned the life and the history of the Christian Church have always been men who have realized that this is the most important thing of all, and they have spent hours in prayer seeking His face and enjoying His love. The man who knows the love of Christ in his heart can do more in one hour than the busy type of man can do in a century. God forbid that we should ever make the activity an end in itself.
Let us realize that the motive must come first, and that the motive must ever be the love of Christ.