It is significant that when our Lord describes the stream of iniquity as it flows out of the heart He begins with the thoughts. For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies… Matthew 15:19.
It is doubtful whether any sin is ever committed until it first incubates in the thoughts long enough to stir the feelings and predispose the will toward it favorably. Even the sudden flash of anger, which of all sins would appear on the surface to have the lowest mental content, is anything but a sudden eruption of the emotions.
The quick-tempered man is one who habitually broods over wrongs and insults and thus conditions himself for the sudden fit of temper that seems to have no mental origin. The heart that has had the benefit of broad, sane thinking on moral questions, especially long meditation upon mans sin, Gods mercy and the goodness of Christ in dying for His enemies, is not conditioned to blow up when occasion arises.
The worst reaction to an affront or an injustice will be annoyance or mild irritation, never a burst of sinful anger.
A. W. Tozer Sermon: The Taming of Anger