What Does the Sixth Commandment Mean?

“You shall not commit adultery” (Exodus 20:14) plainly forbids the betrayal of a marriage, but Scripture and the catechism understand it to guard the whole of God’s good gift of human sexuality—which means it addresses far more than affairs, and it addresses everyone, married or not.

Jesus drove it inward, past the act to the heart: “everyone who looks at a woman with lustful intent has already committed adultery with her in his heart” (Matthew 5:28). So the commandment reaches into thoughts, imaginations, and the eyes—not only the deed. And beyond adultery narrowly, Scripture uses this commandment to forbid all sexual immorality: sex outside of marriage, the misuse of the body, and the whole range of ways we depart from God’s design for sexuality within the one-flesh union of husband and wife (1 Thessalonians 4:3). By this standard, purity is not the achievement of a righteous few but a summons that convicts us all.

Luther’s explanation, characteristically, states the command positively: “We should fear and love God so that we lead a sexually pure and decent life in what we say and do, and husband and wife love and honor each other.” Two things stand out. First, purity is about word and deed and thought, not merely avoiding the worst act—it shapes how we speak, what we look at, how we treat others’ dignity. Second, the commandment doesn’t only forbid; it commands the positive good of faithful, honoring marital love. To love and cherish one’s spouse is itself to keep the Sixth Commandment.

None of this is prudishness or a low view of sex; it is a high view. The commandment fences the gift because the gift is precious (see “Is sex before marriage wrong?” and “What does the Bible say about marriage?”).

And here, as everywhere in the Law, honest self-examination drives us to grace. Few commandments expose the heart like this one. But there is no sexual sin—in act or thought—that Christ’s blood does not cover. He kept this commandment perfectly and forgives fully those who break it, cleansing and restoring rather than condemning.