Donald S. Whitney, Spiritual Disciplines for the Christian Life, 1991, p. 101.
While it is true that God gifts some for ministry as evangelists, He calls all believers to be His witnesses and provides them with both the power to witness and a powerful message. Every evangelist is called to be a witness, but only a few witnesses are called to the vocational ministry of an evangelist. Just as each Christian, regardless of spiritual gift or ministry, is to love others, so each believer is to evangelize whether or not his or her gift is that of evangelist.
Donald S. Whitney, Spiritual Disciplines for the Christian Life, 1991, p. 101.