St Augustine on anger

"... And well do you know, my excellent brother, how, in the midst of such offenses, we must watch lest hatred of any one gain a hold upon the heart, and so not only hinder us from praying to God with the door of our chamber closed, but also shut the door against God Himself; for hatred of another insidiously creeps upon us, while no one who is angry considers his anger to be unjust. For anger habitually cherished against any one becomes hatred, since the sweetness which is mingled with what appears to be righteous anger makes us detain it longer than we ought in the vessel, until the whole is soured, and the vessel itself is spoiled. Wherefore it is much better for us to forbear from anger, even when one has given us just occasion for it, than, beginning with what seems just anger against any one, to fall, through this occult tendency of passion, into hating him. We are wont to say that, in entertaining strangers, it is much better to bear the inconvenience of receiving a bad man than to run the risk of having a good man shut out, through our caution lest any bad man be admitted; but in the passions of the soul the opposite rule holds true. For it is incomparably more for our soul's welfare to shut the recesses of the heart against anger, even when it knocks with a just claim for admission, than to admit that which it will be most difficult to expel, and which will rapidly grow from a mere sapling to a strong tree. Anger dares to increase with boldness more suddenly than men suppose, for it does not blush in the dark, when the sun has gone down upon it..."

Letter to Profuturus