Exposing Adultery to the Light

I once spoke with a man who, by his marital unfaithfulness, had — from a human perspective — ruined not only his marriage and family, but his whole life. As we talked about the wreckage of his sin, he told me the day his wife discovered his adultery was “the darkest day of my life.”

I suggested he reconsider that assessment. That day was not the darkest day of his life, but may have been one of the brightest — because it was the day when the light exposed the darkness of his deceit and hidden sin. The real darkness had not been his wife learning the truth. The real darkness had been the secrecy, deception, and moral compromise that thrived unseen until the light of truth exposed how dark the darkness truly was.

It isn’t easy to have God’s light expose our sin. But as Christians, we must learn to love the light. It’s the evidence of a reprobate mind to hate the light and love darkness, and it’s evidence of a sanctified mind to hate the darkness and love the light.

In a society saturated with sexual immorality — in entertainment, media, politics, and even churches — our moral instincts have become really desensitized. Few of us hate adultery with the seriousness it deserves. If we are to recover a biblical hatred for this sin and a biblical love for holiness and purity, we must shine God’s light on adultery from several angles.

First, to expose the darkness of adultery we need to shine the light on the unity of marriage. Adultery isn’t difficult to define. Biblically, it refers to a sexual relationship with a married person who is not one’s spouse. Whether both parties are married or only one is married, the sin is the same.

But notice something important: adultery only exists in the context of marriage. Where there isn’t marriage, there’s still sexual sin, but strictly speaking it’s not adultery. This means that to grasp the seriousness of adultery, we must understand the nature of marriage itself.

The heart of biblical teaching on marriage is not romance, fulfillment, compatibility, or even happiness. Those may accompany marriage, but they are not its defining essence. The defining reality of marriage is unity.

In Genesis 2:24, God declared that a man shall leave his father and mother and cleave to his wife; the two shall become one flesh. This “one flesh" union makes marriage unlike any other human relationship. Children grow and leave. Friendships change. Vocations shift. But marriage establishes a permanent, covenantal unity between one man and one woman. They do not merely share affection or cooperation; they become one.

Because of this, Scripture calls all people — not only married couples — to honor marriage. Hebrews 13:4 declares, “Let marriage be held in honor among all, and let the marriage bed be undefiled.” Every Christian bears responsibility to protect, respect, and preserve what God has joined together.

Adultery assaults this unity at its core. It seeks to separate that which the Spirit of God has joined together by an act of forbidden sexual union, violating the bodily stewardship God assigns to husband and wife (1 Cor. 7:4). It separates what God has joined together.

This is why Scripture treats adultery with such severity, even allowing it to be grounds for divorce — not because divorce is good, but because adultery is so violently destructive to marital unity. To minimize adultery is to misunderstand marriage itself.

Second, to expose the darkness of adultery we need to shine the light on its root. In the Sermon on the Mount, Jesus says, “But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart” (Matt. 5:28).

The Pharisees focused narrowly on outward compliance. Jesus exposes the heart. The seventh commandment does not merely forbid physical acts; it confronts inward desires, affections, and intentions. Lust, which is sexual coveting, is itself sin.

This reveals something crucial: adultery is not an isolated moral failure. It is one fruit growing from a deeper root — the root of sexual immorality.

Scripture condemns all sexual immorality, not merely the most visible forms. Fornication, pornography, lustful fantasy, homosexuality, abuse, and adultery all spring from the same root: a rejection of God’s design for sexuality within covenant marriage.

Modern culture aggressively resists this clarity. Even within churches, many professing Christians are confused or compromised. For example, in as much as one can trust statistics, statistics suggest that upwards of 80% of young, unmarried Christians have sex before marriage. Some sincerely claim they did not know such activity was sinful. Yet the Scripture doesn’t lack clarity: “This is the will of God, your sanctification: that you abstain from sexual immorality” (1 Thess. 4:3).
God does not calibrate holiness according to cultural norms, hormonal pressures, or social trends. His call is absolute: avoid all sexual immorality. There is no morally neutral sexual expression outside marriage.

Understanding this helps expose how adultery does not suddenly appear in a vacuum. It grows from tolerated lust, unchecked fantasy, unguarded boundaries, and compromised convictions. If the root is not confronted, the fruit will eventually appear.

Third, to expose the darkness of adultery we need to shine the light on consequences. Adultery carries devastating consequences. It wounds marriages, fractures families, destabilizes churches, and erodes trust in communities. Scripture consistently shows that sexual sin carries heavy temporal judgment.

David’s adultery with Bathsheba stands as a sobering example. Though God forgave David when he repented, the consequences remained: the death of his child, violence within his household, rebellion from his sons, and the collapse of peace in his reign (2 Sam. 12–18). His sin cast a long shadow over the remainder of his life.

But Jesus goes further than earthly consequences. He warns of eternal danger. If lust remains unchecked and unrepented, he says it is better to lose an eye or hand than for one’s whole body to be cast into hell (Matt. 5:29–30). These words are not exaggeration. Any sexual sin — including adultery — that is cherished rather than repented of leads to eternal destruction.

Again and again Scripture warns of this reality:

“The sexually immoral…will not inherit the kingdom of God” (1 Cor. 6:9–10).

“The wrath of God is coming” because of sexual immorality (Col. 3:5–6).

“God will judge the sexually immoral and adulterous” (Heb. 13:4).

The portion of the sexually immoral "will be in the lake that burns with fire and sulfur, which is the second death” (Rev. 21:8).

The gospel is gloriously merciful — but repentance is not optional. Persisting in unrepentant sexual sin while claiming Christ is self-deception. The stakes could not be higher.

We will never truly cherish the gospel until we understand the seriousness of the sin from which Christ saves us. Grace becomes cheap when sin becomes small. But when God’s light exposes the depth of our need, the mercy of Christ shines all the brighter.

Adultery thrives in secrecy, rationalization, and cultural accommodation. The church must resist all of this. We exposed the darkness of adultery by shining the light of God’s truth on the unity of marriage, the root of sexual immorality, and the devastating consequences of this sin. This exposure isn’t harshness; it’s love because the goal of exposing sin is not condemnation but redemption. The call of the gospel is not merely to avoid scandal but to love holiness, to cherish covenant faithfulness, to guard the heart diligently, and to walk openly in the light of Christ.