13 Again in selecting for yourself eunuchs and maids and servingmen look rather to their characters than to their good looks; for, whatever their age or sex, and even if mutilation ensures in them a compulsory chastity, you must take account of their dispositions, for these cannot be operated on save by the fear of Christ. When you are present buffoonery and loose talk must find no place. You should never hear an improper word; if you do hear one, you must not be carried away by it.
Abandoned men often make use of a single light expression to try the gates of chastity. Leave to worldlings the privileges of laughing and being laughed at. One who is in your position ought to be serious. Cato the Censor, in old time a leading man in your city, (the same who in his last days turned his attention to Greek literature without either blushing for himself as censor or despairing of success on account of his age) is said by Lucilius to have laughed only once in his life, and the same remark is made about Marcus Crassus.
These men may have affected this austere mien to gain for themselves reputation and notoriety. For so long as we dwell in the tabernacle of this body and are enveloped with this fragile flesh, we can but restrain and regulate our affections and passions; we cannot wholly extirpate them. Knowing this the psalmist says: “be ye angry and sin not;” which the apostle explains thus: “let not the sun go down upon your wrath.” For, if to be angry is human, to put an end to one's anger is Christian.
Source: Letters (New Advent)