of marriage to be grave sins. The gravity of the sin excludes one from sacramental communion' until repented of and forgiven in sacramental confession." Vocation to chastity Church teaching on the sixth commandment includes a discussion on chastity. The Catechism describes chastity as a "moral virtue ... a gift from God, a grace, a fruit of spiritual effort." The Church sees sex as more than a physical act; it also affects body and soul, so the Church teaches that chastity is a virtue all people are called to acquire. It is defined as the inner unity of a person's "bodily and spiritual being" that successfully integrates a person's sexuality with his or her "entire human nature." To acquire this virtue, followers are encouraged to enter into the "long and exacting work" of self-mastery that is helped by friendships, God's grace, maturity and education "that respects the moral and spiritual dimensions of human life." The Catechism categorizes violations of the sixth commandment into two categories: "offenses against chastity" and "offenses against the dignity of marriage". Offenses against chastity The Catechism lists the following "offenses against chastity", in increasing order of gravity according to Kreeft: Lust: the Church teaches that sexual pleasure is good and created by God, who meant for spouses to "experience pleasure and enjoyment of body and spirit". Kreeft says, "Lust does not mean sexual pleasure as such, nor the delight in it, nor the desire for it in its right context." Lust is the desire for sexual pleasure alone, outside its intended purpose of procreation and the uniting of man and woman, body and soul, in mutual self-donation. Masturbation is considered sinful for the same reasons as lust, but is a step above lust in that it involves a physical act instead of a mental one. Fornication is the sexual union of an unmarried man and an unmarried woman. This is considered contrary to "the dignity of persons and of human sexuality" because it is not ordered to the "good of spouses" or the "generation and education of children." Pornography ranks higher because it is considered a perversion of the sexual act that is intended for distribution to third parties for viewing. Prostitution is considered sinful for both the prostitute and the customer; it reduces a person to an instrument of sexual pleasure, violating human dignity and harming society. The gravity of the sinfulness is less for prostitutes