Faithful Hearts in a Faithless World

Text: Exodus 20:14 & Matthew 5:27–30

Main Point:

The Faithful God requires faithful hearts in a faithless world.

Introduction – The Hidden Disease of the Heart

Some sicknesses begin silently — no pain, no fever, but underneath, death is spreading. That’s how sin works.

Adultery doesn’t begin in a hotel room; it begins in the heart — in private imaginations, in unchecked desires, in unguarded moments. And the tragedy of our age is that we celebrate what God calls sin and excuse what He calls idolatry.

Into that moral fog, God speaks from Sinai:

“You shall not commit adultery.” (Exodus 20:14)

He’s not trying to restrict joy; He’s revealing His heart. God gives this command not merely to protect marriage, but to preserve covenant love — because He Himself is the Faithful One.

Centuries later, Jesus pulled back the curtain on what this really meant:

“You have heard that it was said, ‘You shall not commit adultery.’ But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart.” (Matthew 5:27–28)

This command is not just about actions; it’s about affections. It’s not about law-keeping; it’s about love-keeping — love for God, love for others, love that mirrors His loyalty.

Main Point: The Faithful God requires faithful hearts in a faithless world.

I. God’s Command Protects Covenant Love (Exodus 20:14)

Exposition

The seventh commandment — “You shall not commit adultery” — stands like a divine fence around the sacred garden of marriage. The Hebrew word nāʾaph means “to break faith,” not merely “to have sex outside of marriage.” It describes the betrayal of a covenant.

To Israel, marriage was never a private arrangement. It was a public covenant reflecting God’s faithful relationship with His people. That’s why unfaithfulness wasn’t treated as just a personal failure — it was covenant treason.

Throughout Scripture, God uses marital imagery to describe His relationship with His people.

Hosea 2:19–20 “And I will betroth you to me forever. I will betroth you to me in righteousness and in justice, in steadfast love and in mercy. I will betroth you to me in faithfulness. And you shall know the Lord.”

Jeremiah 3:20 “Surely, as a treacherous wife leaves her husband, so have you been treacherous to me, O house of Israel, declares the Lord.’ ”

So when God commands, “You shall not commit adultery,” He’s saying: “Be like Me — steadfast, loyal, faithful — because I am faithful.”

Marriage, then, is not the invention of culture, but the illustration of covenant. It’s designed to show the world how God loves His bride — faithfully, permanently, sacrificially.

Thomas Watson: “The marriage covenant is a copy of that grand covenant made between Christ and His church.”

In giving this command, God reveals not only what He prohibits but what He prizes. He prizes fidelity because He is a covenant-keeping God. Every command reflects His character, and this one reflects His steadfast love and truth (hesed we’emeth).

When we keep this command, we imitate His faithfulness; when we break it, we lie about Him. To be unfaithful in body or heart is to proclaim a false gospel — one that says God doesn’t keep His promises.

That’s why adultery, in any form, is more than moral failure — it’s theological rebellion. It defaces the divine image and denies the covenant reality it was meant to picture.

Application:

Married believers:

Guard the covenant. Faithfulness isn’t just “not cheating.” It’s choosing loyalty every day — in your eyes, your words, your phone, your thoughts.

Cultivate affection intentionally. Pray together. Date each other again. Speak kindly in private and public. Don’t just avoid adultery — pursue intimacy that glorifies God.

Singles and engaged believers:

God’s command isn’t a prison; it’s protection. Purity before marriage prepares you for covenant within marriage. The world says “follow your heart,” but Scripture says, “guard your heart.” Every time you honor God with your desires, you preach His worth.

All believers: God calls His people to mirror His fidelity in all relationships — to be dependable, loyal, and true. The seventh commandment extends beyond the marriage bed — it applies to our integrity, our friendships, our word. To be faithful in the small things is to bear the mark of a faithful God.

The Faithful God requires faithful hearts in a faithless world.

II. Christ’s Exposition Exposes Corrupt Hearts (Matthew 5:27–30)

Matthew 5:27–30 ““You have heard that it was said, ‘You shall not commit adultery.’ But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart. If your right eye causes you to sin, tear it out and throw it away. For it is better that you lose one of your members than that your whole body be thrown into hell. And if your right hand causes you to sin, cut it off and throw it away. For it is better that you lose one of your members than that your whole body go into hell.”

Exposition

In Jesus’ day, the Pharisees treated the law like a fence — as long as you didn’t climb over it physically, you were innocent. But Jesus says the fence runs through the heart.

“Everyone who looks at a woman with lustful intent has already committed adultery with her in his heart.”

The Greek verb blepō means a purposeful, sustained gaze — not the glance that surprises, but the look that lingers. And the phrase (“to lust after”) shows this is deliberate — a desire cultivated, not merely felt.

Jesus is not condemning attraction — He’s condemning covetousness disguised as love. Lust is self-centered desire that treats others as objects for our consumption rather than image-bearers for our honor.

Here’s the radical shift: Sin isn’t just what you do; it’s what you desire. And holiness isn’t just abstaining from wrong things; it’s loving right things.

When Jesus says, “Tear out your eye…cut off your hand,” He’s not calling for mutilation but mortification — the decisive killing of sin. He’s saying: Don’t flirt with sin. Don’t feed sin. Don’t accommodate sin. Kill it.

John Owen: “Be killing sin, or sin will be killing you.”

Thomas Chalmers: “The only way to dispossess the heart of an old affection is by the expulsive power of a new one.”

James 1:14–15 gives the internal anatomy of sin:

“Each person is tempted when he is lured and enticed by his own desire. Then desire when it has conceived gives birth to sin, and sin when it is fully grown brings forth death.”

Lust begins with enticement — a lure, often subtle. Then entertainment — we nurse the thought instead of rejecting it. Then enslavement — desire rules us. And finally, execution — sin kills joy, intimacy, and spiritual vitality.

Jesus exposes this because He loves us. He’s not trying to shame us but to save us — to cut sin out before it consumes us.

Application

Starve what strengthens sin. You can’t kill lust while feeding it through your eyes and ears. What you watch, read, and scroll forms your imagination. Be ruthless about what you allow in.

Feed what strengthens faith. Lust dies when better joy lives. Fill your mind with Scripture, your heart with worship, and your time with service. Delight in the Lord, and you’ll lose taste for counterfeit pleasures.

Fight sin in community. Sin thrives in secrecy. Confess to trusted brothers and sisters. Accountability is not shame — it’s mercy.

Redirect your gaze. When temptation hits, don’t just say “no.” Say “yes” to something greater. Turn your eyes toward Christ, the Faithful One, whose beauty satisfies more deeply than sin ever could.

The Faithful God requires faithful hearts in a faithless world.

The Failure of David (2 Samuel 11)

David, the man after God’s own heart, stayed home when kings went to war. He saw Bathsheba. He looked again. He sent. He took. The chain is painfully simple: sight → desire → action → death.

The man who once sang, “How shall a young man keep his way pure?” forgot his own song. The result? Broken covenant, broken home, broken heart.

“But the thing that David had done displeased the LORD.” (v. 27)

Application

Guard the first glance; it’s rarely the last. You may not control what catches your eye, but you control what holds it. No one falls into adultery by accident — they slide one choice at a time.

Ask: Where am I staying home when I should be at war? Laziness of soul opens the door to lust.

C. The Faithfulness of Joseph (Genesis 39)

In Egypt, Joseph faced temptation daily — “Lie with me.” But his response is the model of covenant faithfulness:

“How then can I do this great wickedness and sin against God?” (v. 9)

He called sin what it was — wickedness — and he called God who He is — worthy. He didn’t stay to negotiate; he fled. And though falsely accused, he gained something better: a clean conscience and God’s presence (v. 21).

Application

Joseph feared God’s holiness more than he feared man’s opinion.

He saw temptation not as an opportunity for pleasure but a threat to fellowship with God.

Faithfulness may cost your reputation — but it preserves your soul.

The Faithful God requires faithful hearts in a faithless world.

IV. God’s Grace Restores Faithful Hearts (Ephesians 5:25–27)

Exposition

No one passes this command unstained. We’ve all looked wrongly, longed wrongly, loved wrongly. But the gospel is that the Faithful One bore the unfaithful’s shame.

“Christ loved the church and gave Himself up for her… to present her holy and without blemish.”

He is the greater Husband who never breaks vows, never turns His gaze away. At the cross, He was treated as the adulterer so that adulterers could be treated as the bride.

Richard Sibbes: “There is more mercy in Christ than sin in us.”

John Flavel: “Christ’s heart beats more for you than your heart beats toward Him.”

Application

Confess, don’t conceal. David’s restoration began when he said, “I have sinned against the Lord.”

Believe, don’t bargain. You can’t earn your way back; the cross already paid the price.

Begin again. God’s grace doesn’t merely pardon — it purifies. He can write new faithfulness where infidelity once reigned.

Conclusion – The Faithful God and the Faithful Heart

The seventh commandment is not an outdated rule; it’s a revelation of divine character. Our God is steadfast in love and faithful in covenant.

In a world where commitment is mocked and purity dismissed, faithfulness is radical worship. When you honor your vows, guard your eyes, and cherish your spouse, you are telling the truth about God.

So ask yourself tonight:

Am I fighting temptation like Joseph — or feeding it like David?

Do I believe that God’s design for love is better than the world’s?

Do I rest in the grace of the Faithful One who never stops loving His bride?

The Faithful God requires faithful hearts in a faithless world.