Jesus Teaches Heart Righteousness

True Righteousness Begins in the Heart
In the Sermon on the Mount, Jesus goes far beyond the surface level of obedience to expose the true source of sin: the heart. While the Law of Moses addressed external actions like murder and adultery, Jesus emphasized the inward attitudes that lead to these sins. In Matthew 5:21–26, He taught that hatred is the root of murder. A heart filled with resentment, jealousy, or bitterness may not act on those feelings, but it is still sinful before God. Jesus called this "murder in the heart" because that’s where every outward action begins.

Self-control, a fruit of the Spirit, begins with identifying our heart's inclinations. Whether the cause is anger, envy, or pride, Christ teaches that reconciliation must be pursued whenever possible. God desires peacemakers. Trying to be reconciled shows humility and a Christlike spirit, even when full restoration may not occur.

Lust Is Adultery of the Heart
Jesus then applied the same principle to the sin of adultery in Matthew 5:27–30. It is not merely the physical act that violates God's will, but also the willful and ongoing desire for someone to whom we are not married. Lust is more than a passing glance; it is a choice to covet, to crave, and to imagine the fulfillment of sinful desire. Jesus' words are clear: "Whoever looks at a woman to lust for her has already committed adultery with her in his heart."

Christ uses strong language—"pluck out your eye," "cut off your hand"—to communicate the seriousness of rooting out sin. He is not calling for literal mutilation but radical repentance. The real problem is not in the eye or hand, but in the heart. Sin must be dealt with decisively and immediately. Colossians 3:5 echoes this call: "Put to death your members which are on the earth: fornication, uncleanness, passion, evil desire." Lust is not harmless. It defiles the mind and, if left unchecked, can destroy lives.

Marriage Is a Sacred Covenant
Jesus continued His teaching in Matthew 5:31–32 by addressing divorce. The Pharisees had twisted Deuteronomy 24:1–4 into a license for casual divorce. Some taught that a man could put away his wife for nearly any reason. Jesus corrected this misuse of Scripture by upholding God’s original intent: marriage is a lifelong covenant. Divorce is only permitted when sexual immorality (fornication) has been committed.

He added that to divorce for any other reason and remarry is to commit adultery. This was a shocking standard, so much so that His disciples later exclaimed in Matthew 19, "If such is the case... it is better not to marry!" Jesus' words remind us that God has always viewed marriage as a solemn and binding relationship. Human laws may permit no-fault divorce, but divine law holds us accountable to a higher standard.

Honesty in Speech Reflects the Heart
In Matthew 5:33–37, Jesus addressed the issue of oaths and personal integrity. Under the Old Law, people made oaths to affirm the truth of their words. But many abused this practice by swearing falsely or using oaths to manipulate. Jesus instructed His followers to avoid the need for oaths altogether by being people of their word. "Let your 'Yes' be 'Yes,' and your 'No,' 'No.'"

A Christian should be so honest that no extra words are needed to verify his intentions. Swearing by heaven, earth, or anything else is unnecessary if your word is trustworthy. Truthfulness, like the other traits Jesus taught, starts in the heart. An honest heart produces honest speech.

Conclusion
Jesus calls us to a righteousness that exceeds outward forms and reaches into the inner person. Sin does not begin with the hand or the eye—it begins in the heart. Whether it is anger, lust, dishonesty, or selfishness, Jesus teaches us to confront and conquer sin where it starts. He demands purity, integrity, and commitment from the inside out.

Sermon Outline: "Jesus Teaches Heart Righteousness"

I. The Root of Murder

• Matthew 5:21–26: Hatred is condemned as "murder in the heart."
• Reconciliation is commanded where possible.
• God's judgment applies to attitude, not just action.

II. Lust and Adultery of the Heart

• Matthew 5:27–30: Lust is spiritual adultery.
• Radical steps (figuratively) must be taken to remove temptation.
• Colossians 3:5: Put to death sinful desires.

III. God's Law on Divorce and Remarriage

• Matthew 5:31–32: Only fornication permits divorce.
• Matthew 19:1–9: Jesus reinforces the sanctity of marriage.
• God holds the guilty and those who marry them accountable.

IV. Truthfulness Without Oaths

• Matthew 5:33–37: Let your word be your bond.
• Christians should not need to swear to be believed.
• Honest hearts produce honest speech.

Call to Action: Examine your heart. Are you holding onto anger, harboring lust, or speaking dishonestly? Christ calls you to purity not only in deed but in desire. Let today be the day you surrender your heart to Jesus. Repent, be cleansed, and commit to walking in righteousness from the inside out.

Lesson prepared by Bobby Stafford, church of Christ at Granby, MO