9 Take no well-curled steward to walk with you, no effeminate actor, no devilish singer of poisoned sweetness, no spruce and smooth-shorn youth. Let no theatrical compliments, no obsequious adulation be associated with you. Keep with you bands of widows and virgins; and let your consolers be of your own sex. The character of the mistress is judged by that of the maid. So long as you have with you a holy mother, so long as an aunt vowed to virginity is at your side, you ought not to neglect them and at your own risk to seek the company of strangers. Let the divine scripture be always in your hands, and give yourself so frequently to prayer that such shafts of evil thoughts as ever assail the young may thereby find a shield to repel them. It is difficult, nay more it is impossible, to escape the beginnings of those internal motions which the Greeks with much significance call προπάθειαι that is 'predispositions to passion.' The fact is that suggestions of sin tickle all our minds, and the decision rests with our own hearts either to admit or to reject the thoughts which come. The Lord of nature Himself says in the gospel:— “out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies.” It is clear from the testimony of another book that “the imagination of man's heart is evil from his youth,” and that the soul wavers between the works of the flesh and of the spirit enumerated by the apostle, desiring now the former and now the latter. For
From faults no mortal man is wholly free;
The best is he who has but few of them.
And, to quote the same poet,
At moles men cavil when they mark fair skins.
To the same effect in different words the prophet says:— “I am so troubled that I cannot speak,” and in the same book, “Be angry and sin not.” So Archytas of Tarentum once said to a careless steward: “I should have flogged you to death had I not been in a passion.” For “the wrath of man works not the righteousness of God.” Now what is here said of one form of perturbation may be applied to all. Just as anger is human and the repression of it Christian, so it is with other passions. The flesh always lusts after the things of the flesh, and by its allurements draws the soul to partake of deadly pleasures; but it is for us Christians to restrain the desire for sensual indulgence by an intenser love for Christ. It is for us to break in the mettlesome brute within us by fasting, in order that it may desire not lust but food and amble easily and steadily forward having for its rider the Holy Spirit.
Source: Letters (New Advent)