John Newton, writing in a letter to a correspondent on controversy (Works of John Newton, 1:270-272):
Of all people who engage in controversy, we, who are called Calvinists, are most expressly bound by our own principles to the exercise of gentleness and moderation. . . .
The Scriptural maximum, that “The wrath of man worketh not the righteousness of God,” is verified by daily observation. If our zeal is embittered by expressions of anger, invective, or scorn, we may think we are doing service to the cause of truth, when in reality we shall only bring it into discredit. . . .
Whatever it be that makes us trust in ourselves that we are comparatively wise or good, so as to treat those with contempt who do not subscribe to our doctrines, or follow our party, is a proof and fruit of a self-righteous spirit. Self-righteousness can feed upon doctrines, as well as upon works; and a man may have the heart of a Pharisee, while his head is stored with orthodox notions of the unworthiness of the creature and the riches of free grace.