Spiritual adultery is unfaithfulness to God. It is having an undue fondness for the things of the world. Spiritually adultery is analogous to the unfaithfulness of one’s spouse: “ ‘But like a woman faithless to her lover, even so have you been faithless to me, O house of Israel,’ says the LORD” (Jeremiah 3:20; see also Isaiah 1:21; 57:8; Ezekiel 16:30).
The Bible tells us that people who choose to be friends with the world are an “adulterous people” having “enmity against God” (James 4:4–5). The “world” here is the system of evil under Satan’s control (John 12:31; Ephesians 2:2; 1 John 5:19). The world system, with its contrived and deceitful scheme of phony values, worthless pursuits, and unnatural affections, is designed to lure us away from a pure relationship with God. Spiritual adultery, then, is the forsaking of God’s love and the embracing of the world’s values and desires (Romans 8:7–8; 2 Timothy 4:10; 1 John 2:15–17).
Spiritual adultery includes any form of idolatry. In the Old Testament, the children of Israel tried to mix the worship of other gods such as Baal with that of God (Judges 3:7; 1 Kings 16:31–33; Jeremiah 19:5). In doing so, Israel became like an adulterous wife who wanted both a husband and another lover (Jeremiah 9:2; Ezekiel 6:9; 16:32). In the New Testament, James defines spiritual adultery as claiming to love God while cultivating friendship with the world (James 4:4–5). The person who commits spiritual adultery is one who professes to be a Christian yet finds his real love and pleasure in the things that Satan offers. For believers, the love of the world and the love of God are direct opposites. Believers committing spiritual adultery may claim to love the Lord, but, in reality, they are captivated by the pleasures of this world, its influence, comforts, financial security, and so-called freedoms.
The concept of spiritual adultery against God is a major theme throughout the Old Testament (Isaiah 54:5; Jeremiah 3:20; Ezekiel 16:15–19). This theme is illustrated especially well in the book of Hosea. The prophet’s wife, Gomer, symbolizes the infidelity of the children of Israel (Hosea 2:2–5; 3:1–5; 9:1). Hosea’s commitment to Gomer symbolizes God’s faithful, patient love with His erring people.
Jesus said, “No one can serve two masters. Either you will hate the one and love the other, or you will be devoted to the one and despise the other” (Matthew 6:24). The Bible exhorts us, “Do not love the world or anything in the world. If anyone loves the world, love for the Father is not in them. For everything in the world—the lust of the flesh, the lust of the eyes, and the pride of life—comes not from the Father but from the world” (1 John 2:15–16). Believers must echo the words of the old hymn: “The world behind me, the cross before me; no turning back.”
“As obedient children, do not conform to the evil desires you had when you lived in ignorance. But just as He who called you is holy, so be holy in all you do; for it is written: ‘Be holy, because I am holy’ ” (1 Peter 1:14–16). Spiritual adultery is like trying to straddle the fence with one foot in the world and the other heaven. We cannot have both. As Jesus warned the church in Laodicea, “I know your deeds, that you are neither cold nor hot. I wish you were either one or the other! So, because you are lukewarm—neither hot nor cold—I am about to spit you out of my mouth” (Revelation 3:15–16).
The love of the world is primarily an attitude of one’s heart, and we can cast away worldliness by cultivating a new affection. To avoid spiritual adultery, “set your hearts on things above, where Christ is, seated at the right hand of God. Set your affection on things above, not on things on the earth” (Colossians 3:2, KJV).
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.