Why does faithfulness in marriage and love matter?
The short answer
The Sixth Commandment — "you shall not commit adultery" — protects the faithfulness and beauty of married love and, more broadly, calls everyone to chastity: ordering our sexuality toward genuine love rather than using people. It forbids adultery and unfaithful acts, while pointing positively to the goodness of self-giving, faithful love.
Full explanation
At its most direct, this commandment guards marriage. Adultery — being sexually unfaithful to one's spouse, or with someone else's — is a serious betrayal: it breaks a solemn covenant, wounds a spouse and often children, and treats a sacred bond as disposable. Jesus underscores how seriously God takes marital union: "what God has joined together, let no one separate." Faithfulness isn't a quaint ideal; it's the very thing that makes married love trustworthy and life-giving.
But Jesus, as with the other commandments, takes it deeper than outward acts. He teaches that adultery begins in the heart: "everyone who looks at a woman with lust has already committed adultery with her in his heart." So this commandment isn't only about a physical act of betrayal; it's about the whole way we regard and treat other people — whether we see them as persons to love or as objects to use.
That's why the Church understands the Sixth Commandment as the broad call to chastity — the virtue that integrates our sexuality with real love, lived according to one's state in life (married, single, or consecrated). Several specific questions flow from it, each with its own fuller treatment: the meaning of chastity, the place of sex within marriage (and so the teaching on sex before marriage and cohabitation), pornography, same-sex attraction, and questions of marriage's nature. (See the dedicated entries on each.)
Underneath all the specifics is a positive vision the negatives are protecting: sexuality is a good gift, powerfully tied to love and life, and the commandment exists to keep that gift serving genuine self-gift rather than being hollowed out into use and betrayal. God himself describes his covenant with his people in the language of a faithful marriage — so faithfulness in love isn't an arbitrary rule; it reflects the very character of God.
Why this matters
Faithfulness is the soil real love grows in. Betrayal — in body or in heart — devastates trust, families, and children, while the culture often treats sex as casual and commitment as optional. The Sixth Commandment insists that people are worth fidelity and worth being loved rather than used. Lived well, it protects marriages and trains every person, married or not, to regard others as persons rather than objects.
Myth Common misunderstanding
One misunderstanding is that this commandment only forbids the physical act of adultery, so lustful use of others "in the head" doesn't count. Jesus says otherwise — it begins in the heart. The opposite misunderstanding hears the commandment (and the Church's sexual teaching) as anti-sex; in fact it protects sex because it is good and meaningful, meant for faithful, self-giving love.
Scripture connections
- Exodus 20:14 — "you shall not commit adultery," the commandment itself.
- Matthew 5:27-28 — Jesus extends it to lust in the heart, not only the outward act.
- Matthew 19:6 — "what God has joined together, let no one separate," the seriousness of marital union.
- 1 Corinthians 6:18-20 — "flee from sexual immorality"; the body as a temple of the Holy Spirit.
- Hosea 2:19-20 — God's faithful, "married" love for his people, the model of fidelity.
Church teaching references
Reflect
Beyond avoiding outright betrayal, where might you be treating someone as an object to be used rather than a person to be loved — and what would faithful, self-giving love ask of you instead?