13 And do not be surprised if, in connection with such endurance, I seek another test of fortitude in the soul. For to be indifferent to food and drink and a soft bed, we see is to many no hard task, especially at least to such as are of a rough habit of life and have been brought up in this way from early youth, and to many others also; bodily discipline and custom softening the severity of these laborious practices: but insult, and abuse, and coarse language, and gibes from inferiors, whether wantonly or justly uttered, and rebukes vainly and idly spoken both by rulers and the ruled— this is what few can bear, in fact only one or two here and there; and one may see men, who are strong in the former exercises, so completely upset by these things, as to become more furious than the most savage beasts.
Now such men especially we should exclude from the precincts of the priesthood. For if a prelate did not loathe food, or go barefoot, no harm would be done to the common interests of the Church; but a furious temper causes great disasters both to him who possesses it, and to his neighbours. And there is no divine threat against those who fail to do the things referred to, but hell and hell-fire are threatened against those who are angry without a cause. As then the lover of vainglory, when he takes upon him the government of numbers, supplies additional fuel to the fire, so he who by himself, or in the company of a few, is unable to control his anger, but readily carried away by it, should he be entrusted with the direction of a whole multitude, like some wild beast goaded on all sides by countless tormentors, would never be able to live in tranquillity himself, and would cause incalculable mischief to those who have been committed to his charge.
Source: On the Priesthood (New Advent)