The sixth commandment is “You shall not commit adultery,” as formulated in Exodus 20:14. Like the preceding two commandments, this formulation gives a very plain and direct reference to one reality (in this case, adultery) under which there are several layers – some of which we may not be fully aware. In the simplicity of The New Saint Joseph Baltimore Catechism, the deeper implications are given to include all acts of impurity and immodesty, whether in appearances, words, thoughts, or actions, both with others or alone. In a positive light, we can consider this commandment as a call to true and “chaste” love that respects every person (including self) for who they are in God’s sight.
The depth of the commandment is well illustrated by Jesus himself in the Sermon on the Mount, when he says that the man who looks on a woman with lust has already committed adultery with her in his heart (see Matthew 5:28). Certainly, the act of committing adultery is plainly defined as a married person being unfaithful to his/her spouse through an extra-marital relationship. However, Jesus words give this commandment its fullest expression as a call to “chastity,” or what might be simply defined as a right expression of love in one’s own heart according to that one’s state in life. When looking directly at the paragraphs of the Catechism of the Catholic Church, the subject of chastity comprises a major portion of the treatment of this commandment (paragraphs 2337-2359), such that rightly living this command is far more than simply avoiding immoral sexual behavior – but a practicing of true love within all our relationships, upholding the true dignity of every person and never “using” ourselves or another for gratification of desires. Minding the content of examples of such “use,” I strongly urge your going through the paragraphs of the catechism that are cited below for further explanation of examples that offend against this true life of chaste love, minding that each one of us, no matter what our particular state of life and vocation is, is called to be rightly chaste in accord with our particular vocation.
Given that this commandment tends to be viewed only by what it prohibits, it is important to spend a moment speaking to what this commandment invites and truly strengthens. For from the beginning, God willed that a man should leave his father and mother and be joined to his wife, that they become one flesh (see Genesis 2:24). This union of man and woman in holy matrimony is a profound gift from God – as married couples participate in the work of creation through their love for one another: both in their union to one another that symbolizes God’s love for the Church, and in their bringing about of new human life through procreation. Given both the sacred nature of this gift and its beauty as a sharing in God’s creative work, the sacred union between a man and woman is always to be upheld and ought to be rightly promoted. That said, it is important to recognize that every type of non-marital sexually active relationship is understood as sinful – as such actions weaken and even destroy the beauty of God’s gift. Likewise, the altering or prevention of the true goods of this union (by using contraception) undermine the gift of God – closing the couple off to both the union to which they are called as married couples and to the capacity to procreate. Accordingly, it is important that we emphasize the nature of God’s gifts in marriage, seeking to help couples to become more aware and ready to embrace how God want to bless them and aid them – onto the chaste love which is theirs by God’s gift.
For further reading: In the Catechism of the Catholic Church, paragraphs 2331 - 2400 gives detailed teaching on this commandment, giving beautiful teaching on the nature of marriage and family as gifts from God.