Chastity (& Sins of Unchastity)

As a virtue is that virtue which (a.) excludes all indulgence of and all voluntary pleasure arising from the sexual appetite in the case of single persons; (b.) controls the use of such appetite according to the dictates of right reason in the case of married persons. (Definition from A Catholic Dictionary, 1951)
 

References in Scripture:

• Blessed are the clean of heart: for they shall see God." Matthew 5:8
• "Take heed to keep thyself, my son, from all fornication, and beside thy wife never endure to know a crime." Tobias 4:13
• "For this is the will of God, your sanctification; that you should abstain from fornication; That every one of you should know how to possess his vessel in sanctification and honor: Not in the passion of lust, like the Gentiles that know not God: For God hath not called us unto uncleanness, but unto sanctification. Therefore, he that despiseth these things, despiseth not man, but God, who also hath given his holy Spirit in us." 1 Thes 4:3-5,7-8
• "Impose not hands lightly upon any man, neither be partaker of other men's sins. Keep thyself chaste" 1 Tim 5:22
• "Dearly beloved, I beseech you as strangers and pilgrims, to refrain yourselves from carnal desires which war against the soul" 1 Peter 2:11
• "Then the angel Raphael said to him: Hear me, and I will shew thee who they are, over whom the devil can prevail. For they who in such manner receive matrimony, as to shut out God from themselves, and from their mind, and to give themselves to their lust, as the horse and mule, which have not understanding, over them the devil hath power" Tobias 6:16-17
• "Wherefore God gave them up to the desires of their heart, unto uncleanness, to dishonor their own bodies among themselves. Who changed the truth of God into a lie; and worshipped and served the creature rather than the Creator, who is blessed for ever. Amen. For this cause God delivered them up to shameful affections. For their women have changed the natural use into that use which is against nature. And, in like manner, the men also, leaving the natural use of the women, have burned in their lusts one towards another, men with men working that which is filthy, and receiving in themselves the recompense which was due to their error. And as they liked not to have God in their knowledge, God delivered them up to a reprobate sense, to do those things which are not convenient" Romans 1:24-28
• "Juda, therefore add to Onan his son: Go in to thy brother's wife and marry her, that thou mayst raise seed to thy brother. He knowing that the children should not be his, when he went in to his brother's wife, spilled his seed upon the ground, lest children should be born in his brother's name. And therefore the Lord slew him, because he did a detestable thing" Genesis 38:8-10
• "Every soul that shall commit any of these abominations, shall perish from the midst of his people. Keep my commandments. Do not the things which they have done, that have been before you, and be not defiled therein. I am the Lord your God" Leviticus 18:29-30
• "For if you live according to the flesh, you shall die: but if by the Spirit you mortify the deeds of the flesh, you shall live" Romans 8:13
• "Know you not that the unjust shall not possess the kingdom of God? Do not err: neither fornicators, nor idolaters, nor adulterers, Nor the effeminate, nor liers with mankind, nor thieves, nor covetous, nor drunkards, nor railers, nor extortioners, shall possess the kingdom of God" 1 Corinthians 6:9-10
• "Now the works of the flesh are manifest, which are fornication, uncleanness, immodesty, luxury, Envies, murders, drunkenness, revellings, and such like. Of the which I foretell you, as I have foretold to you, that they who do such things shall not obtain the kingdom of God. But the fruit of the Spirit is, charity, joy, peace, patience, benignity, goodness, longanimity, Mildness, faith, modesty, continency, chastity. Against such there is no law" Galations 5:22-23
• "The Lord knoweth how to deliver the godly from temptation, but to reserve the unjust unto the day of judgment to be tormented. And especially them who walk after the flesh in the lust of uncleanness, and despise government, audacious, self willed, they fear not to bring in sects, blaspheming. But these men, as irrational beasts, naturally tending to the snare and to destruction, blaspheming those things which they know not, shall perish in their corruption, Receiving the reward of their injustice, counting for a pleasure the delights of a day: stains and spots, sporting themselves to excess, rioting in their feasts with you: Having eyes full of adultery and of sin that ceaseth not: alluring unstable souls, having their heart exercised with covetousness, children of malediction: These are fountains without water, and clouds tossed with whirlwinds, to whom the mist of darkness is reserved." 2 Peter 2:9-10,12-14,17
• "As Sodom and Gomorrha, and the neighboring cities, in like manner, having given themselves to fornication, and going after other flesh, were made an example, suffering the punishment of eternal fire" Jude 1:7
• "Let us walk honestly, as in the day: not in rioting and drunkenness, not in chambering and impurities, not in contention and envy: But put ye on the Lord Jesus Christ, and make not provision for the flesh in its concupiscences" Romans 13:13-14
• "Know you not that your bodies are the members of Christ? Shall I then take the members of Christ, and make them the members of an harlot? God forbid. Or know you not, that he who is joined to a harlot, is made one body? For they shall be, saith he, two in one flesh. But he who is joined to the Lord, is one spirit. Fly fornication. Every sin that a man doth, is without the body; but he that committeth fornication, sinneth against his own body." 1 Cor 6:15-18
• "Neither let us commit fornication, as some of them committed fornication, and there fell in one day three and twenty thousand." 1 Corinthians 10:8
• "But fornication, and all uncleanness, or covetousness, let it not so much as be named among you, as becometh saints: Or obscenity, or foolish talking, or scurrility, which is to no purpose; but rather giving of thanks." Ephesians 5:3-4
• "Mortify therefore your members which are upon the earth; fornication, uncleanness, lust, evil concupiscence, and covetousness, which is the service of idols. For which things the wrath of God cometh upon the children of unbelief" Colossians 3:5-6
• "But I say to you, that whosoever shall look on a woman to lust after her, hath already committed adultery with her in his heart." Matthew 5:28

Church Teaching:

• "Chastity takes its name from the fact that reason "chastises" concupiscence, which, like a child, needs curbing, as the Philosopher states (Ethic. iii, 12). Now the essence of human virtue consists in being something moderated by reason, as shown above (I-II, 64, 1). Therefore it is evident that chastity is a virtue." St. Thomas Aquinas, Summa Theologica (13th century), Is Chastity a Virtue?
• "In fine, in spite of what others may wish to assert and spread abroad by word of mouth or in writing, let husband and wife resolve: to stand fast to the commandments of God in all things that matrimony demands; always to render to each other the assistance of mutual love; to preserve the honor of chastity; not to lay profane hands on the stable nature of the bond; to use the rights given them by marriage in a way that will be always Christian and sacred, more especially in the first years of wedlock, so that should there be need of continency afterwards, custom will have made it easier for each to preserve it" Encyclical On Christian Marriage by Pope Pius XI, 1930
• "Every care and solicitude must be used to have the young soldiers of the sacred army appreciate, love, and preserve chastity, because the choice of the priestly state and perseverance in it depend in great part on this virtue. Being exposed to greater dangers, chastity must be solidly possessed and proved at length. Let seminarians, therefore, inform themselves about the nature of ecclesiastical celibacy, of the chastity that they must observe and of the obligations it brings with it,[82] and let them be warned of the dangers they may meet" Apostolic Exhortation of Pope Pius XII To The Clergy of the Entire World, 1950
• "Holy virginity and that perfect chastity which is consecrated to the service of God is without doubt among the most precious treasures which the Founder of the Church has left in heritage to the society which He established." Encyclical On Consecrated Virginity by Pope Pius XII, 1954

Summary

Scripture is very explicit on the subject of chastity. Those who live unchaste lives, which includes fornicators, homosexuals, those who lust after others or otherwise living unclean lives, cannot be saved unless they confess these sins and give up these lifestyles. Note this includes the vice of masturbation.

As we can see from past Church teaching, one of the ways to practice perfect chastity is through holy virginity.