1. Because it goes against God’s original design
The prohibition against adultery doesn’t make sense until we understand God’s original design for sexual expression within the confines of marriage. From the beginning, God established a blueprint for the family. He saw that it was not good for man to be alone, and he created woman. Adam and Eve together reflected the image of God in their relationship of trust and love.
In Genesis 2:24-25, we read: “Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh. And the man and his wife were both naked and were not ashamed.” God’s design was for one man to be united with one woman as one flesh. Man would leave his father and mother in order to form a new family. In the innocence and purity of the garden of Eden, they would live together naked and not feel any shame.
2. Because it destroys marriages and families
The glorious picture of marital bliss in the garden was shattered by human sin. When the first couple sinned against God, they became separated from God. The marriage covenant is still powerful, but because of sin, it is a fractured version of what God originally intended. Trust is broken. Marriages are imperfect. Many fall apart.
Throughout Old Testament history, we see how marriage was damaged as a result of sin in the world. Men mistreated women by betraying them or taking multiple wives. Adultery became commonplace.
A well-known story of adultery in the Old Testament is King David and Bathsheba in 2 Samuel 11. Here we see a strong king who followed after God’s heart but fell to the sin of adultery. David, the giant-killer and mighty warrior, saw from the rooftop of his palace a beautiful woman bathing. What the king wanted, the king got. Disregarding the fact she was married to Uriah—a soldier on the front lines of his army fighting for Israel—David slept with her.
After Bathsheba informed him she was pregnant, David sent for Uriah, thinking he could cover up his sin by having Uriah spend the night with his wife. But Uriah was a faithful servant who extolled the virtues of his king and his soldiers. Even David’s plot to use alcohol to dull Uriah’s senses didn’t work. Uriah didn’t sleep with his wife, and the secret pregnancy would soon be known. The lust that led David to adultery next led him to lie and then led him to kill. In a remarkable display of depravity, David sent Uriah to the front lines and ordered the military commander to pull back during the fighting so Uriah would die.
David did not get away with this act of cruelty. God’s law was clear, and God’s law was intended to guide his people to a life filled with joy. David’s sin reaped severe consequences for his family and his country.
3. Because it damages a picture of the gospel
You may wonder what God’s law about adultery has to do with the gospel. In Galatians 3:24, Paul wrote that “the law was our guardian until Christ came, in order that we might be justified by faith.” If we apply this verse about the law in general to the specific law against adultery, we see that this Commandment (like a guardian) was meant to protect marriage. It protects the design of what God established from the beginning.
The law also protected marriage as a picture of the gospel. The apostle Paul wrote that husbands are to love their wives as Christ loved the church (Eph. 5:25). Marriage is connected to Christ in that it paints a picture of our relationship with God.
In Matthew 19:5-6, Jesus reaffirmed the Old Testament’s vision of a man leaving his family to become one flesh with his wife. This passage demonstrates the fact that Christ came to fulfill the law, not abolish it. It also demonstrates the importance of fidelity in marriage. Jesus went so far as to say, “What therefore God has joined together, let not man separate.”
God is the One who joins man and woman together. Marriage is more than a document that deals with assets, rights and obligations. It is the physical, lasting union of a man and woman for life. Adultery is the tearing apart of the “one flesh” God has established. That’s why it damages people emotionally, psychologically and spiritually.
4. Because it is an expression of spiritual adultery
Physical adultery may be against a spouse, but there is always a spiritual component that is against God. That’s why David, who sinned against Bathsheba and her husband, when confessing his sin, cried out to God for forgiveness: “Against you, you only, have I sinned” (Ps. 51:4). Physical adultery is an expression of spiritual adultery.
In Scripture, God often describes his relationship with his people in terms of a marriage covenant. The expectation is love and fidelity. God is faithful and constantly pursuing his people, but his people “cheat” on him by running after idols.
Through the prophets Hosea and Ezekiel, God described his relationship with the nation of Israel in graphic terms. God said that he covered the nakedness of Israel and entered into a covenant with “her,” giving the nation a female description in order to compare his relationship with Israel to that of a groom and bride. He bestowed wealth and gifts on his beloved, but the nation chose to worship idols. Ezekiel 16:15 says: “But you trusted in your beauty and played the whore because of your renown and lavished your whorings on any passerby; your beauty became his.”
The seriousness with which God takes our sin is a sign that God desires to receive glory and love from us. He desires to have a relationship with his people, and this relationship must be exclusive.
As believers, our relationship with Christ is now described in terms of a bride and groom. In James 4:4, we read that friendship with the world is hostility toward God. Those who give themselves over to worldly patterns of thought and behavior are “adulteresses”—serious language from a God serious about loving his people!