Custom is indeed in everything hard to resist. It possesses an enormous power of attracting and seducing the soul. In the cases where a man has got into a fixed state of sentiment, a certain imagination of the good is created in him by this habit; and nothing is so naturally vile but it may come to be thought both desirable and laudable, once it has got into the fashion. Take mankind now living on the earth. There are many nations, and their ambitions are not all the same. The standard of beauty and of honour is different in each, the custom of each regulating their enthusiasm and their aims.
This unlikeness is seen not only among nations where the pursuits of the one are in no repute with the other, but even in the same nation, and the same city, and the same family; we may see in those aggregates also much difference existing owing to customary feeling. Thus brothers born from the same throe are separated widely from each other in the aims of life. Nor is this to be wondered at, considering that each single man does not generally keep to the same opinion about the same thing, but alters it as fashion influences him.
Not to go far from our present subject, we have known those who have shown themselves to be in love with chastity all through the early years of puberty; but in taking the pleasures which men think legitimate and allowable they make them the starting-point of an impure life, and when once they have admitted these temptations, all the forces of their feeling are turned in that direction, and, to take again our illustration of the stream, they let it rush from the diviner channel into low material channels, and make within themselves a broad path for passion; so that the stream of their love leaves dry the abandoned channel of the higher way and flows abroad in indulgence.
It would be well then, we take it, for the weaker brethren to fly to virginity as into an impregnable fortress, rather than to descend into the career of life's consequences and invite temptations to do their worst upon them, entangling themselves in those things which through the lusts of the flesh war against the law of our mind; it would be well for them to consider that herein they risk not broad acres, or wealth, or any other of this life's prizes, but the hope which has been their guide.
It is impossible that one who has turned to the world and feels its anxieties, and engages his heart in the wish to please men, can fulfil that first and great commandment of the Master, “You shall love God with all your heart and with all your strength.” How can he fulfil that, when he divides his heart between God and the world, and exhausts the love which he owes to Him alone in human affections? “He that is unmarried cares for the things of the Lord; but he that is married cares for the things that are of the world.”
If the combat with pleasure seems wearisome, nevertheless let all take heart. Habit will not fail to produce, even in the seemingly most fretful, a feeling of pleasure through the very effort of their perseverance; and that pleasure will be of the noblest and purest kind; which the intelligent may well be enamoured of, rather than allow themselves, with aims narrowed by the lowness of their objects, to be estranged from the true greatness which goes beyond all thought.
Source: On Virginity (New Advent)