Lust
Lust is generally spoken of as impurity. Impurity is a shameful vice because it changes a good and beautiful power into sin. This vice is opposed to chastity which Our Lord tells us makes men like angels. Chastity is defined by St. Thomas as the virtue which regulates sensual desires and pleasures for the married and absolutely forbid them to the unmarried. Hence, lust or impurity is a seeking for unlawful pleasures, especially through the sense of touch. Sins of impurity defile both the soul and the body, which is the temple of the Holy Spirit, and is destined at the resurrection of the body to be glorified forever.
The modest ear is offended by the very names of sins committed through lust, such as adultery, fornication, incest, rape, birth control, abortion, and solitary sin. St. Paul says of these, "Let it not so much as be named among you." (Eph. 5:3). We name them only to inspire horror for them.
Impurity wraps itself around all our senses and through them enters our soul. It blinds us to spiritual values, darkens our minds, weakens our wills and leads us to place a created good before God. We may commit sins of the mind by impure thoughts; sins of the eyes by giving in to curiosity, by impure looks at persons, pictures or things, by sinful reading; sins of the ears by listening to indecent speech, lewd and suggestive stories, jokes, songs, etc.; sins of the nose by enjoyment of sensuous odors; sins of the mouth by impure words and songs and failure to chide evil talk; sins of the lips by sensuous kissing; sins of the hands by sinful touches, fondling, embraces, or other sinful actions; sins of the heart by impure desires and failure to repress impure sensations when unintentionally aroused; sins which we occasion in others; sins arising from companions.
Indulgence in impurity in any way is simply contrary to God's plan. Married persons, though lawfully enjoying the pleasures of sex which are sanctified by the marital union, must also observe chastity according to their state by a reasonable self-control. Any misconduct with regard to others is doubly grievous for the married. Whether chastity is the consecrated chastity of the priesthood or the cloister, the chastity of the unmarried, or the chastity of wedlock, we must see it as a dedication of our powers to the service of God. Then it will be an influence for uplifting the world about us.
Impurity is often followed by other evils. It blinds the mind, perverts the will and hardens the heart. It causes inconstancy in repentance, brings about aversion to God because His law forbids the desired pleasure, and fosters an excessive love of things of this world. It causes mental anxiety through fear of future punishment. It often leads to diseases and insanity. Disobedience, scandal and loss of faith may follow in its wake. Insincere Confessions and sacrilegious Communions are often the result of impure practices. Lust or impurity probably causes the loss of more souls than any other sin.
Vulgarity, sensuality and impurity are nurtured by idleness, by attachment to ease and comfort, by excess in eating and drinking. Obscene and suggestive literature, scandalous movies and T.V. programs, immodest pictures, sinful dancing, immodest clothing and companions may lead us into sinful actions. Too frequent association with the opposite sex, as in the case of persons "going steady" without expectation of early marriage, often occasions mortal sins of impurity.