On anger

We must, with God's help, eradicate the deadly poison of anger from the depths of our souls. So long as the demon of anger dwells in our hearts ... we can neither discriminate what is good, nor achieve spiritual knowledge, nor fulfill our good intentions, nor participate in true life.... Nor will we share in divine wisdom even though we are deemed wise by all men, for it is written: Anger lodges in the bosom of fools (Eccles. 7:9). Nor can we discriminate in decisions affecting our salvation even though we are thought by our fellow men to have good sense, for it is written: Anger destroys even men of good sense (Proverbs 15:1). Nor will we be able to keep our lives in righteousness with a watchful heart, for it is written: Man's anger does not bring about the righteousness of God (James 1:20)....

If, therefore, you desire to attain perfection and rightly pursue the spiritual way, you should make yourself a stranger to all sinful anger and wrath. Listen to what St. Paul enjoins: Rid yourselves of all bitterness, wrath, anger, clamor, evil speaking, and all malice (Eph. 4:31). By saying 'all' he leaves no excuse for regarding any anger as necessary or reasonable. If you want to correct your brother when he is doing wrong or punish him, you must try to keep yourself calm; otherwise you yourself may catch the sickness you are seeking to cure and you may find that the words of the Gospel now apply to you: Physician, heal yourself (Luke 4:23), or Why do you look at the speck of dust in your brother's eye, and not notice the beam in your own eye? (Matt. 7:3).

No matter what provokes it, anger blinds the soul's eyes, preventing it from seeing the Sun of righteousness.... Whether reasonable or unreasonable, anger obstructs our spiritual vision. Our incensive power can be used in a way that is according to nature only when turned against our own impassioned or self-indulgent thoughts.  St. John Cassian