“You shall not commit adultery.” (Exodus 20:14)
Two consenting adults. Nobody robbed. Nobody hit. Nobody killed.
Ask a modern reader to point to the victim in adultery and many will struggle. It looks like the most private sin on the list—a matter between grown people who’ve decided something for themselves.
And yet God placed this commandment here, between murder and theft, in a list of 10. Of all the things two people could do behind a closed door, why does this one belong beside killing?
What the Word Actually Covers
Two Hebrew words worth knowing
Na’aph — the word in this commandment. It means adultery in the strict sense: sexual unfaithfulness where a marriage is involved.
Zanah — a broader word covering prostitution and sexual immorality generally.
So the commandment names the narrower sin. Does that mean everything else is permitted?
No—and for the same reason we’ve cited throughout this series. Each commandment names the outermost and gravest form of a sin, and in doing so forbids the whole family of sins beneath it. “Do not murder” reaches down to contempt. “Do not commit adultery” reaches down to every misuse of sex, and Jesus says so explicitly.
There’s also a second use of na’aph that will matter later. The prophets use this word constantly for idolatry—describing Israel as an unfaithful wife. Hold that thought.
Why Does Adultery Earn a Place in the Ten?
Four reasons, and they add up.
1. Because marriage is a covenant, not contract
This distinction does more work than any other in the whole discussion, so it’s worth being clear.
| Category | A CONTRACT | A COVENANT |
|---|---|---|
| What is exchanged | Services, goods, money | Persons. You give yourself. |
| Why you keep it | Because the other party is delivering | Because you promised |
| How it ends | When the terms aren’t met, or when it expires | It isn’t designed to end |
| Who is involved | The two parties, and perhaps a lawyer | The two parties, the community, and God as witness |
Malachi says it directly. Confronting men who were discarding their wives, he tells them the LORD was witness between them and the wife of their youth—“your companion and your wife by covenant” (Malachi 2:14). God was standing there when the promise was made.
That’s why adultery isn’t merely a disappointment or broken arrangement. It’s a breach of covenant—which is the category of sin the Bible treats most severely from Genesis to Revelation. And the covenant is made in the presence of a witness who doesn’t forget.
2. Because marriage began before the law did
Like the Sabbath, marriage is a creation ordinance. It appears in Genesis 2, before Israel, before the law, before sin: “Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh” (Genesis 2:24).
This matters because it settles what kind of institution marriage is. It isn’t a social custom that societies invented and may therefore reinvent. It’s part of how humanity was built. When Jesus was asked about divorce, He didn’t begin with Moses. He went back to Genesis and quoted this verse (Matthew 19:4–6).
3. Because there are always more than two people involved
The “consenting adults” framing assumes only the people in the room count. A covenant doesn’t work like that.
There’s a spouse who consented to something entirely different. There are children, born and unborn, whose world runs on the assumption the ground beneath them is solid. Malachi, in the same passage, says God was seeking godly offspring (Malachi 2:15)—the family is where the covenant reaches the next generation, which is exactly what the fifth commandment depends on.
Attack the seventh commandment and the fifth has nothing left to travel through.
Why sex, specifically?
It’s worth asking why sexual unfaithfulness gets its own commandment when other betrayals don’t. A friend who breaks a confidence has broken faith. A business partner who walks away has broken a promise. Why is this one in the 10?
Scripture’s answer: sex isn’t simply an activity people do. It’s covenant-making in bodily form. “The two shall become one flesh” isn’t a poetic way of describing pleasure; Paul takes the phrase seriously enough to argue a man who joins himself to a prostitute becomes one body with her (1 Corinthians 6:16). Something real happens, whether or not either person intends it.
That’s why sexual sin isn’t tidied away as a private preference. The act makes a statement—I give myself to you entirely—and it makes that statement even when the people involved mean nothing by it. Adultery therefore involves telling a lie with your body while your mouth is still committed elsewhere.
Christopher JH Wright puts the matter helpfully: the biblical objection to sexual sin isn’t that sex is dangerous but that it’s significant. Trivialise something significant and we don’t make it harmless; we make ourselves unable to use it for what it was for.
4. Because marriage is a picture of something
This is the deepest reason, and it’s distinctively Christian.
Paul quotes Genesis 2:24 about one flesh and then says something startling: “This mystery is profound, and I am saying it refers to Christ and the church” (Ephesians 5:32). Marriage was designed, from the beginning, as a working model of the union between Christ and His people.
So adultery isn’t only the betrayal of a person. It’s the defacing of a signpost. Michael Horton argues this is why Scripture reaches so readily for marital language when describing idolatry—the two sins are the same sin at different scales.
So Where’s the Victim?
The honest answer: there are more victims than the question assumes.
| WHO IS HARMED | HOW |
|---|---|
| The betrayed spouse | Not merely hurt feelings. A person who gave themselves under a promise discovers the promise was conditional after all. |
| The children | They lose the assumption that the world is stable, usually at an age when they cannot articulate what has gone. |
| The other party | Whatever the language of consent, one person has been used for something that could never be given honestly. |
| The community | Every marriage in a community rests partly on the assumption that such promises are generally kept. |
| The person who does it | Paul says sexual sin is uniquely self-directed—a sin “against his own body” (1 Corinthians 6:18). |
| The witness of the church | When it happens among Christians, the world concludes something about the God whose name they carry. |
It’s worth noticing how radical Israel’s law was on this point. Surrounding legal codes treated adultery mainly as an offence against a husband’s property, with penalties the wronged man could waive in exchange for compensation. Israel’s law treated it as a sin against God that no payment could settle. Joseph, refusing Potiphar’s wife, doesn’t say “I would be wronging your husband”. He says, “How then can I do this great wickedness and sin against God?” (Genesis 39:9).
The same point can be made about the world the New Testament entered. In Greek and Roman society a married man’s use of slaves, prostitutes and concubines was so ordinary as to be beneath comment; fidelity was a demand made of wives, not of husbands. When the apostles told husbands to be faithful to their wives and to love them as Christ loved the church, they weren’t restating a shared cultural value. They were saying something their neighbours found strange, and it was one of the things outsiders noticed about the early Christians.
Jesus Makes It Wider
“You have heard that it was said, ‘You shall not commit adultery.’ But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart.” (Matthew 5:27–28)
This verse needs careful handling.
What Jesus is and isn’t saying
Not: that noticing someone is attractive is adultery. The Greek phrase behind “with lustful intent” carries the sense of looking in order to desire—a cultivated, purposeful look, not an involuntary one.
Not: that sexual desire is dirty. The same Bible contains the Song of Songs and tells married couples not to deprive one another (1 Corinthians 7:5).
Yes: that a person can be reduced, in the privacy of the imagination, to an object assembled for someone else’s use. That is the sin—and the other person never consented to it, never knew, and cannot object.
Notice who is protected. Jesus is speaking into a culture where a man could dismiss a wife with relative ease and where blame fell overwhelmingly on women. He puts the responsibility squarely inside the man’s own heart.
The remedy He then gives—tear out the eye, cut off the hand—is deliberate overstatement, and every commentator recognises it as such. Jesus isn’t recommending self-mutilation. He’s saying the cost of dealing with this seriously will feel like that, and should be paid anyway.
Where This Bites Today
Pornography
This is adultery of the heart, industrialised and delivered on demand. It trains a person, repetition by repetition, to treat human beings as items that exist for consumption and can be dismissed when they stop being useful. That’s precisely the disposition the commandment forbids, and it doesn’t stay in the imagination—it reshapes how a person sees the actual people in their life.
Almost nobody escapes this alone, and secrecy is the mechanism that keeps it running. Tell one trustworthy person. Get practical barriers in place. Where it has become compulsive, involve a pastor and, where appropriate, a professional. Shame keeps people stuck; confession is the exit.
The affair that never became physical
Adultery isn’t only a body in the wrong bed. A marriage can be hollowed out by intimacy given elsewhere—the conversations, the confidences, the messages sent late, the person at work who gets the best of you while your spouse gets what is left.
A useful test: is there anything in this friendship you wouldn’t want your spouse to read? The instinct to hide is almost always the first honest signal.
Faithful in body, absent in every other way
It’s possible to keep this commandment in the narrowest sense while breaking everything it was protecting. A spouse who’s never unfaithful and never present hasn’t kept a covenant.
Following the rule that governs this series, the commandment doesn’t only forbid betrayal. It requires cherishing.
Sex outside marriage
The New Testament word porneia covers sexual activity outside marriage generally, and the apostles address it constantly—not because they were prudish, but because they were writing to converts from a culture in which it was ordinary and unremarkable. Their consistent position is that the one-flesh union belongs inside the covenant that gives it meaning.
Cohabitation raises the same question in modern dress. The difficulty isn’t the living arrangement in itself but what it usually signifies: the union without the covenant, and therefore the intimacy without the promise that makes it safe.
Why this commandment feels hardest today
It’s worth naming the assumption that makes this commandment sound cruel to modern ears.
Our culture largely holds that desire is identity: that what people want most deeply reveals who they truly are, and that any restriction on it is therefore a restriction on the self. On that assumption, a rule about sex isn’t a rule about behaviour at all. It’s an attack on a person’s existence.
The Bible says something different, and it says it about every desire, not only this one. Desire is real, it’s powerful, and it isn’t sovereign. We’re not identical with what we want, and we’re not obliged to obey it. That’s either an insult or a liberation, depending on whether we’ve ever been ruled by a desire we couldn’t switch off.
It’s also worth saying the commandment isn’t a rule about who we’re permitted to be attracted to. It’s a rule about what we do, and what we cultivate. Nobody in Scripture is condemned for what they didn’t choose to feel.
A word to single readers
This commandment isn’t a married person’s commandment. It binds everyone, and it also protects everyone: single people are the ones most often used by those who break it.
And it’s worth saying plainly: singleness isn’t a waiting room. Jesus was single. Paul was single, and he wrote about it as a gift rather than a deficiency (1 Corinthians 7:7). A church that treats marriage as the normal Christian outcome has misread its own Bible, and it makes the seventh commandment far harder to keep for the people carrying the most weight.
What the Commandment Requires
| WHAT IT FORBIDS | WHAT IT THEREFORE REQUIRES |
|---|---|
| Sexual unfaithfulness in a marriage | Wholehearted faithfulness—body, attention and affection |
| Cultivated lust, and using people in the imagination | Guarding the eyes and the mind, and treating people as persons |
| Sexual activity outside the covenant | Chastity before marriage and fidelity within it |
| Intimacy transferred to someone outside the marriage | Deliberate investment in the marriage you have |
| Speech that trivialises sex or degrades people | Speech that honours marriage and protects reputations |
| Tempting others, or profiting from their fall | Protecting the vulnerable, especially the young and the isolated |
| Neglect dressed up as technical fidelity | Cherishing a spouse, actively and visibly |
The Husband Who Was Betrayed
Now to the reason the prophets kept using ‘adultery’ to mean ‘idolatry’.
God doesn’t describe Israel’s unfaithfulness in the language of a disappointed employer or a frustrated legislator. He describes it in the language of a betrayed husband—across Hosea, Jeremiah 3 and Ezekiel 16. He describes it at length and with a rawness that’s uncomfortable to read.
And then Hosea receives the instruction that has no parallel anywhere in ancient literature. His wife has gone. He is told to go and get her back, and to pay for her (Hosea 3:1–2). God is describing His own response to covenant betrayal. And He doesn’t choose divorce. He chooses redemption at His own cost.
That’s the shape of the gospel, and it’s why marriage was made to picture it. The Bible opens with a wedding in a garden and closes with a wedding feast at the end of history (Revelation 19:7–9). Everything in between is the story of a faithful husband and an unfaithful people.
Which is also why, when a woman caught in adultery was dragged in front of Jesus, the one person present with a genuine right to throw a stone didn’t throw it. He sent her accusers away and then told her to leave her life of sin (John 8:1–11). The account’s place in the manuscripts has long been debated, but the portrait is unmistakably His: neither excusing the sin nor destroying the sinner.
How This Commandment Is Actually Kept
Not by willpower alone, and not by pretending desire away.
It’s kept by covenant-keeping becoming the thing we admire rather than the thing we endure. By deciding in advance where the lines are, because nobody makes good decisions at 11 at night. By living close enough to other Christians that secrets are hard to keep. And, for those of us who’re married, by pouring into the covenant we have rather than nursing a quiet inventory of what it lacks.
Sinclair Ferguson describes faithfulness as learned rather than felt. Nobody arrives at it. It is built, in the ordinary and unglamorous decisions of years, by people who’ve decided promises are the kind of thing that get kept.
And if you’re reading this having already broken it, the account of Hosea is the point of the article rather than a decoration on the end of it. God’s response to covenant betrayal wasn’t a lecture or a dismissal. It was a purchase.
Next in this series: the eighth commandment. Having protected life and the covenant in which life begins, the Decalogue turns to what a person makes with their hands.
Tough Questions, Honest Answers
Is divorce ever permitted, and may a divorced Christian remarry?
God says plainly He hates divorce (Malachi 2:16), and Jesus taught that what God has joined together must not be separated. But Scripture does recognise circumstances in which a marriage has already been broken by the other party. Jesus names sexual unfaithfulness as an exception (Matthew 19:9), and Paul addresses the case of a believer deserted by an unbelieving spouse, saying the believer is not enslaved in such cases (1 Corinthians 7:15). Reformed churches have historically recognised these two grounds, and most also treat sustained physical danger as a form of desertion, since a spouse who is destroying the other has already abandoned the covenant in substance. Where a marriage has ended on such grounds, we hold remarriage is permitted. This is an area where the details of a particular situation matter enormously, and no article should be a substitute for a wise pastor who knows the case.
Why did the patriarchs have more than one wife—does the Bible allow polygamy?
The Bible records polygamy without approving it, and this distinction is essential to reading the Old Testament. Genesis 2 establishes one man and one woman as one flesh, and Jesus goes back to that verse rather than to the patriarchs when settling the question. Notice also how the accounts are written: every polygamous household in Scripture is portrayed as a disaster, from Abraham’s to Jacob’s to David’s to Solomon’s, whose many wives are explicitly blamed for turning his heart away. The law regulated the practice as it regulated other things it did not create, limiting harm in a society it found rather than endorsing what it found. By the New Testament the expectation is stated plainly: an overseer is to be the husband of one wife.
Is pornography grounds for divorce?
Christians answer this differently, and we would resist a quick ruling either way. The argument that it is grounds treats Jesus’ words about adultery of the heart as covering it, and points out that habitual, concealed use is a genuine betrayal of the covenant. The argument against treating it as automatic grounds notes that Jesus’ exception clause concerns an act rather than a desire, and that if every heart-level breach dissolved a marriage very few would survive. Pornography is a serious sin against marriage. It must be named as such and never minimised, but the first response should be confession, accountability and help rather than dissolution. Where it is unrepentant, deceptive over years, or has escalated into something worse, the situation changes and the couple need real pastoral care rather than an article.
Is it wrong for an engaged couple to live together before the wedding?
Yes, though the reason is worth understanding rather than simply asserting. The New Testament consistently locates sexual union inside marriage, and cohabitation almost always means taking the union without the covenant that gives it its meaning and its safety. Engagement is a promise to make a promise; it is not the promise itself, and a significant number of engagements end. There is also a practical dimension worth weighing: many couples cohabit for financial reasons and genuinely intend to marry, and where the arrangement is truly separate and temporary the question becomes one of wisdom and of how it appears to others rather than of direct disobedience. Those situations are real, and they are best worked out honestly with a pastor rather than by quietly deciding that nobody will ask.
Does the seventh commandment have anything to say about same-sex relationships?
It does, by way of the pattern it protects. The commandment guards the one-flesh union established in Genesis 2, which Jesus reaffirmed as male and female by the Creator’s design, and the New Testament addresses same-sex sexual relationships directly in Romans 1 and 1 Corinthians 6 among other places. We should be honest that revisionist readings of those passages exist and are argued by serious people, chiefly on the grounds that the biblical writers were addressing exploitative practices rather than committed partnerships; we do not find that persuasive, since the reasoning in Romans 1 appeals to creation rather than to consent. What we would resist strongly is the habit of treating this as the sin that defines the commandment, when the passage in 1 Corinthians 6 lists it alongside greed, drunkenness and slander, and then tells the whole church that such were some of you. Anyone who holds this position and speaks about it without tenderness has misunderstood the God who gave the commandment.
If my spouse has been unfaithful, am I required to forgive and stay?
Forgiveness and reconciliation aren’t the same thing, and confusing them has done great damage. You’re commanded to forgive, in the sense of releasing the debt to God rather than nursing it and repaying it. You’re not commanded to remain in the marriage: Jesus named this specific sin as a ground on which the innocent party may lawfully separate. Many marriages do survive adultery, and some become stronger, but that outcome requires genuine repentance from the one who broke the covenant rather than mere regret at being discovered. Take time, involve your church, and be very wary of anyone—on either side—who pressures you towards a quick decision.
Does this commandment apply to single people?
Entirely. It forbids sexual activity outside the covenant of marriage, which addresses single people directly, and it forbids the cultivated lust Jesus described, which addresses everyone. It also protects single people, who’re most often on the receiving end when someone else breaks it. The positive duties fall on the unmarried too: honouring other people’s marriages, refusing to be the person through whom one is broken, and treating others as persons rather than possibilities. And the church has an obligation here as well, since a congregation that offers single Christians no real friendship, welcome or place is asking them to carry this commandment alone.
CONTINUE THE SERIES: THE TEN COMMANDMENTS
This post is part of our series working through the Ten Commandments. It follows Why God Gave the 10 Commandments—And Why These 10?, The First Commandment: Why Does God Demand Exclusive Worship?, The Second Commandment: Why Does God Forbid Idols?, The Third Commandment: What Does “Taking God’s Name in Vain” Mean?, The Fourth Commandment: Why Did God Command a Day of Rest?, The Fifth Commandment: Why Must We Honour Our Parents?, and The Sixth Commandment: Why Does God Forbid Murder?.
Related Reads
- Why God Gave the 10 Commandments—And Why These 10?
- The First Commandment: Why Does God Demand Exclusive Worship?
- The Second Commandment: Why Does God Forbid Idols?
- The Third Commandment: What Does “Taking God’s Name in Vain” Mean?
- The Fourth Commandment: Why Did God Command a Day of Rest?
- The Fifth Commandment: Why Must We Honour Our Parents?
- The Sixth Commandment: Why Does God Forbid Murder?
- The Eighth Commandment: Why Does God Forbid Stealing?
- The Ninth Commandment: Why Does God Care About Truth?
- The Tenth Commandment: Why Does God Care About What We Desire?
- How To Break Free From Pornography: A Christian Perspective
- Is Living Together Before Marriage Really a Problem?
- Grounds For Divorce: Does the Bible Affirm More Than Two?
