You shall not commit adultery.
Like the Sixth Commandment, the Seventh consists of only two Hebrew words: lo tinap – “no adultery.” It is meant to prohibit any person or immoral act to do damage to the relationship between husband and wife. The biblical pattern for marriage is that of an exclusive relationship between “a man and a woman who commit themselves to each other in covenant for life and, on the basis of solemn vows, become ‘one flesh’ physically (Genesis 2:24; Malachi 2:14; Matthew 19:4-6)” (Waltke, 429).
The Bible uniformly condemns adultery. Abimelech considered it a great sin (Genesis 20:9). Joseph called adultery a “wicked thing” (Genesis 39:9). Job connects adultery to the acts of murderers and thieves (Job 24:13-17). Jeremiah viewed it as an outrageous act (Jeremiah 29:23). In Proverbs the adulterer is portrayed as a fool (6:32; 2:15-19; 5:1-23; 6:20-35; 7:1-27). In Leviticus 18 faithfulness within marriage is codified as a means for Israel to keep herself pure from the defiling influences of the pagans.
Like all of the commandments, the seventh applies to a whole category of sins. Specifically it prohibits all sexual sins; sins which damage the marriage relationship and defile the people of God. The privileged responsibility of sex is inseparably linked to the responsibility of marriage and family. The creation order dictates that sexual intimacy is linked to a man leaving the household of his parents and clinging to his wife. Therefore there is no legitimate expression of sexual intimacy outside of marriage between one man and one woman. Jesus called lustful thoughts a violation of the seventh commandment (Matthew 5:27-28). So the seventh commandment forbids both immoral acts and thoughts.
Since God called his people to himself he has compared the relationship to a marriage (Hosea; Isaiah 57; Ezekiel 23; Jeremiah 3; Ephesians 5:22ff). The analogy is meant to teach us that God’s relationship to us is one of covenant exclusivity. Therefore, to go after other gods whether they are literal idols or idols of the heart is an act of spiritual adultery. And this is the dilemma for all of us. Each of us have wandered after idols. We have all from one degree to another pursued adultery with gusto.
And this is why the faithfulness of Christ is so necessary. For it is not our faithfulness which binds us to God. Rather, it is God’s unwavering faithfulness through Christ which binds us to him. As Paul tells us in Ephesians 5, Christ is the faithful Bridegroom who even now is purifying us that he might present us to himself one day holy without any blemish (Ephesians 5:22ff). By his perfect covenant faithfulness and sacrificial death Jesus cleanses adulterers.