Deuteronomy 5:18 Commentary: The Seventh Commandment's Reach

The Ten Commandments (Deuteronomy 5:6, 21) are presented as Israel's covenant charter, spoken directly by God at Horeb and written on two stone tablets. They follow Yahweh's self-identification as the one who brought Israel out of Egypt, the command against adultery is therefore grounded in redemption, not merely social utility.

In ancient Israel, marriage was more than a private arrangement. It was the basic unit of family, inheritance, and tribal identity. Adultery, defined as a man's sexual intercourse with a married woman, struck at this order. The woman's husband held exclusive sexual rights within the marriage; violating them was a theft of honor and a threat to lineage. Leviticus 20:10 prescribes the death penalty for both parties, underscoring how seriously the community treated the offense. The adulterer "destroys his own soul" (Proverbs 6:32).

The wider ancient Near East also condemned adultery, but Israel's law was distinctive for three reasons. First, the covenant context gave sexual faithfulness to one's spouse a theological weight: Yahweh's relationship with Israel was itself pictured as a marriage, so adultery became a metaphor for idolatry (Jeremiah 3, Hosea). Second, the command applied to men and women alike in principle, though enforcement in practice fell unevenly. Third, the Decalogue placed the prohibition within a list that begins with exclusive loyalty to God and includes commands about the neighbor's life, marriage, property, and reputation. Adultery, like murder and theft, violates the neighbor's good.

Jesus later deepened the command by tracing it to its root in the heart (Matthew 5:27, 28). But even before his teaching, faithful readers like Wesley asked: "Hast thou not looked on a woman so as to lust after her?" The commandment already demanded more than outward correctness, it called for a pure heart, a theme echoed in the Psalms and Prophets.

The consulted sources note no significant textual variants for Deuteronomy 5:18. The Cambridge Bible observes that in Deuteronomy the command uses ve-lo ("and not") to connect it with the surrounding prohibitions, whereas Exodus 20:14 has the simpler lo ("not"). This is a stylistic difference, not a substantive change in meaning.

The seventh commandment has been central to Christian ethical teaching from the earliest centuries. The Didache and other early church manuals included it in catechesis for new believers. Augustine devoted a sermon to the commandment, arguing that it forbids both the act and the desire, anticipating Jesus' teaching in the Sermon on the Mount. The medieval church developed a detailed penitential system around sexual sins, often using this text as a starting point. The Reformers, Luther and Calvin, stressed that the command exposes human inability and drives sinners to grace. In modern times, the commandment has been applied to issues of pornography, emotional affairs, and the violation of marital trust. Across all traditions, the verse has been read as a gift that protects marriage and points to the need for inner transformation through the Spirit.

Three-point outline

1. The command protects the covenant. Adultery is not merely a personal sin; it breaks the marriage bond that God established and blessed. The prohibition stands at the center of the Decalogue because faithful relationships mirror God's faithful love for His people.
2. The command exposes the heart. As Jesus demonstrated, the outward act is the fruit of an inner disposition. Lust, covetousness, and disregard for the neighbor's good are already violations of the command's spirit.
3. The command calls to restoration. For those who have broken this command, in act or heart, there is forgiveness. The same God who gave the law also provides cleansing and the power to walk in newness of life.

Five-point outline

1. Adultery as covenant breaking (Deuteronomy 5:18; Leviticus 20:10)
2. Adultery begins in the heart (Matthew 5:27, 28)
3. Adultery damages the community (Proverbs 6:32, 33)
4. Adultery and idolatry are linked (Hosea 1, 3)
5. Grace reaches the adulterer (John 8:1, 11; 1 Corinthians 6:9, 11)

Illustration hooks

• A marriage where one partner has been unfaithful, the long road of rebuilding trust. The command isn't a restriction; it's a guard for a gift.
• The way people excuse small disloyalties, a hidden message, a secret friendship, a wandering eye, and do not see they are on a path the command warns against.
• A couple renewing their vows years after infidelity, as a picture of covenant grace.

Questions your congregation is asking

• Does this command mean I can never remarry after divorce? (This text alone does not answer; the wider biblical teaching must be consulted.)
• What about lust in the heart, is that as serious as the act itself? Jesus says yes, and Wesley presses the same point.
• How do I find forgiveness if I have committed adultery? The gospel offers full cleansing, but the relational consequences are often severe and lasting.

This command seems clear on the surface, do not commit adultery. But Jesus' teaching in Matthew 5:27, 28 shows that the commandment reaches deeper than the outward act. As you discuss, consider how this command protects marriage, how it exposes what is in the heart, and how grace speaks to both the guilty and the self-righteous.

Discussion questions

1. Read Deuteronomy 5:18 in its context (verses 6, 21). What do you notice about how the command is positioned among the other commands?
2. The Hebrew word na'aph (נָאַף) specifically means a man having intercourse with another man's wife. Does that definition limit the command, or does it give a clear target?
3. Jesus says that looking with lust is already adultery in the heart (Matthew 5:27, 28). Is he changing the command or showing what it always meant?
4. Wesley's Notes asks probing questions: "Hath thy heart conceived no unclean thought? Hast thou not looked on a woman so as to lust after her?" How do these questions change how you read the seventh command?
5. Proverbs 6:32 says the adulterer "destroys his own soul." What kinds of destruction does adultery cause, to the individual, the family, the community?
6. Why does the Bible connect adultery to idolatry (think of the prophets Hosea, Jeremiah, Ezekiel)? What does that link tell us about God's heart?
7. The woman caught in adultery (John 8) received both truth and grace. How does this story shape your understanding of the command and the gospel?