What does Exodus 20:14 mean?

God's covenant with the nation of Israel (Exodus 19:5–6; 20:1) is introduced with a concise set of laws: the Ten Commandments. These include rules on how the people are to treat God (Exodus 20:1–11), and how to treat one another (Exodus 20:12–13, 15–17). The principles in these early laws establish a foundation for the rest of the law of Moses (2 Chronicles 5:10).

Adultery is sexual contact with someone other than one's spouse. The term is usually applied to married people, while unmarried sexual contact would be "fornication" or simply "sexual immorality." The same is true here; this commandment uses a term specifically referring to violating a marriage through illicit sex. Marriage between one man and one woman is humanity's oldest relationship model (Genesis 1:27–28; 2:24–25). This system is rooted in mutual support and respect, as well as loyalty. Taking sex—the most intimate human behavior—outside of that arrangement dishonors the spouse and insults the Creator who instituted marriage.

Marriage is fundamental to a culture's existence. It is the cornerstone of the family which is mankind's basic social unit. This makes violating marriage a serious problem. This was especially true in the ancient world where trust and commitment were essential to survival. Women needed to know that husbands were caring for them and them alone. Husbands needed to know that the children they supported were their offspring. Both needed assurance that their relationship was sacred and valuable. Under the Mosaic covenant, blatant adultery could be punished with death (Leviticus 20:10; Deuteronomy 22:22).

Marriage is also sacred because of its parallels to God's relationship with mankind. The Lord will occasionally compare the nation of Israel to His bride (Jeremiah 2:2–3, 32). This makes idolatry and worship of false gods adultery—as offensive to God as a spouse is dishonored by a cheating partner (Jeremiah 3:1; Ezekiel 16:30–34). The church of believers in Christ is considered the "bride of Christ" (2 Corinthians 11:2–3; Ephesians 5:22–33).

Jesus will point out that this commandment is not limited to physical acts. Lusts and imaginations towards others are also sins in God's eyes (Matthew 5:27–28).