Introduction

I love the refrain of that song: “The strength to follow Your commands could never come from me.” As we’re going to see today, the strength to follow what God commands truly cannot come from ourselves.

We’re continuing in Jesus’s Sermon on the Mount. The next verse after where we left off last time is Matthew 5:27. I want to remind you that when Jesus was preaching, there were no section breaks or paragraph breaks. This verse comes immediately after what He was just saying before. So, let’s remember where we have been.

Remembering Where We Have Been

You might recall how Jesus began His sermon with the Beatitudes—statements of who is truly blessed. When we talked about murder and anger, it hearkened back to Jesus’s statement, “Blessed are the peacemakers, for they will be called sons of God.” Jesus’s command was, “You have heard it said, ‘Do not murder,’” and He taught that the same heart that would murder is an angry heart. So, we shouldn’t just avoid murder externally; Jesus is getting to the heart of anger. He actually said, “Don’t just not be angry, but be a peacemaker,” because the peacemakers will be called sons of God. That means if you are a Christian—if you are part of God’s family—you should be a peacemaker.

In the verse right before that, Matthew 5:8, Jesus said, “Blessed are the pure in heart, for they shall see God.” All Christians will see God, and Jesus is saying that Christians are pure in heart. God demands purity from the heart, not just external purity. He sees your heart and demands purity from the inside. That’s the overarching theme of today’s lesson: sin occurs in the heart, and God demands purity of the heart.

Fast forward, and we have this whole section where Jesus is preaching. It started in Matthew 5:20, which says, “Unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven.” That might not mean much to us unless we remember who the scribes and Pharisees were. These were Israel’s teachers, and they made sure everybody knew they were the most righteous, godly people around. Imagine hearing Jesus say, “Unless your righteousness is more than the most righteous person you know, you’ll never enter the kingdom of heaven.”

Exceeding the Righteousness of the Scribes and Pharisees

After that statement in Matthew 5:20, Jesus goes on. In verse 21, then verse 27, 31, 33, 38, 43, you see the phrase repeated: “You have heard it said…” For instance, verse 21: “You have heard it said by those of old, ‘Do not murder.’” Then verse 27: “You have heard it said, ‘Do not commit adultery.’” And on it goes.

Who is Jesus quoting? It sounds like He might be quoting the Old Testament, but actually, He’s quoting what the scribes and Pharisees had taught. He’s not correcting the Old Testament. He is correcting the scribes and Pharisees. They had it all wrong. They thought they could keep God’s law well enough to be righteous before Him, and when they realized they couldn’t keep it perfectly, they changed the rules. They focused on an external interpretation that made them feel good about themselves and told everyone else to follow that. As long as they kept those outward rules, they felt they were righteous.

But Jesus gave God’s view of their law-keeping. He saw right through their hypocrisy, just like He sees right through us. The scribes and Pharisees said, “Don’t murder,” and felt good because they weren’t actual murderers—at least not directly. They said, “Don’t commit adultery,” but they redefined it in ways the Bible never allowed. They cared about externals—what people could see—but God sees the heart.

Jesus’s assessment of the scribes and Pharisees appears in Matthew 23. He says, “Woe to you, scribes and Pharisees, hypocrites! You are like whitewashed tombs…” A tomb might appear clean on the outside but inside is a dead, rotting carcass. He said that’s what they were like: they appeared godly but inside were full of dead men’s bones and uncleanness. They looked righteous on the outside, but God saw their hearts. And so Jesus says repeatedly, “You have heard it said, but I say to you,” getting to the heart of the issue.

He called them hypocrites. Outwardly, they looked righteous, but inwardly they were full of hypocrisy and lawlessness. We saw it when we discussed anger. They said, “Don’t murder,” but they were content to hate in their hearts. Jesus taught that hatred in your heart is guilt before God. And now, Jesus goes further and continues to address the heart.

Adultery Begins in the Heart

Is your heart off-limits? As we keep going through the Sermon on the Mount, it’s going to get harder—actually impossible—without God changing us from the inside. It reveals how sinful we really are if we only look at the outside. But that’s good if it causes us to put our hope in the right place, confess sin, and repent, because God is faithful to forgive.

Look at Matthew 5:27: “You have heard it said, ‘You shall not commit adultery.’” The teachers of the law used this to prove their righteousness: “I don’t commit adultery.” But they had redefined adultery completely. The seventh commandment says, “You shall not commit adultery.” Adultery is a horrific evil. It is doing with someone else what is only appropriate to do with your spouse. God reserved that for marriage. Outside of that, it is sin.

The Pharisees thought, “If I don’t commit the external act of adultery, I’m okay.” But Jesus is not disagreeing with “Do not commit adultery.” He’s saying you shouldn’t feel comfortable if that’s your only standard. In verse 28, He 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.”

Self-justifying man focuses on external behavior. But God, who justifies man, focuses on the heart. If you look with lustful intent, you’ve already committed adultery in your heart. This isn’t just seeing something once by accident—our world is filled with images that want to grab your attention. It’s the second look and your intent that matters. Think of King David with Bathsheba. He noticed her on the roof, and instead of turning away, he kept looking and pondering. That led to so many devastating sins—actual adultery, murder, and chaos in his family. But even the initial lustful intent was already adultery in his heart.

This is sobering. It means that if you look and keep looking, if you desire what’s off-limits in your mind or heart, you commit adultery internally. Even if nobody knows but you, it is still sin before God.

God Sees the Heart

We talked last week about crushes: a crush is a desire. Sometimes people put posters on the wall or images on their phones, fixating on someone who isn’t their spouse. Everyone around you might say that’s normal, but what does Jesus say? It’s adultery in your heart. Don’t feel good just because you’re meeting some external standard. The sin of adultery isn’t only the outward act; it happens in the heart.

The same principle applies to other areas too. Obeying your parents with an inward grumble is disobedience in the heart. Avoiding murder while harboring anger is murder in the heart. Going to church, taking notes, and giving the right answers in a small group, yet having no desire to please God in your heart, is still sin. God sees right through it.

Maybe this sounds extreme or you feel condemned if you already see heart sin in your life. This is from Jesus, the One who made you and who sets the standard. He says the heart matters, so if you find sin there, confess it. Repent. There is joy and cleansing in that. First John 1:9 says if you confess your sins, He is faithful and just to forgive and cleanse. As long as you are breathing, there is hope for forgiveness.

Self-Justification vs. God’s Justification

The Bible is clear: adulterers will not inherit the kingdom of God. But Scripture also shows us that real adultery occurs in the heart. By that standard, we are all adulterers, every one of us. Self-justification says, “Look at what I do and don’t do externally; I must be good enough.” Meanwhile, you could be full of lustful intent and remain guilty before God. But when God justifies, He forgives your sin and declares you righteous, placing Jesus’s righteousness on you and taking your sin, placing it on Jesus. God changes you, not just on the outside, but from the inside. You become a new creation, transferred from the domain of darkness into the kingdom of His beloved Son.

So your first response isn’t just “I need to try harder.” You should say, “I need a Savior.” By this standard, none of us can stand. If lustful intent is adultery, then we all need salvation. God justifies sinners who realize their guilt and turn to Him. He cleanses us from the heart.

This changes everything about how we live, including how we consume media, what books we read, and what images we allow ourselves to see. It affects how we relate to others, how we dress, how we conduct ourselves when it comes to dating or any relationship. This isn’t about how close you can get to sin without crossing a line; it’s about fleeing sin from the heart.

Our Need for a Savior

First Corinthians 6:9 says clearly that the unrighteous will not inherit the kingdom of God. It lists the sexually immoral, idolaters, adulterers, thieves, the greedy, drunkards, revilers, swindlers, and declares they will not inherit the kingdom. That should sober every one of us. We all see ourselves in that list in one way or another, especially at the heart level.

But then Paul adds, “Such were some of you.” The church isn’t made of people who never fit those categories; it’s made of people who used to be defined by those sins but have been washed, sanctified, and justified in the name of Jesus. If you realize, “I am an adulterer,” and you confess and turn to God, you can be washed, sanctified, and justified. That’s real hope. God takes your sin and gives you Christ’s righteousness. You are no longer standing on your own but with Christ.

Closing Encouragement

All who are saved will now walk in obedience from the heart. We will confess sins, including those hidden in our hearts, and pursue true purity.

Let’s go to our discussion groups and think about these questions: Have I been focused only on external behavior, or do I care about what is going on in my heart? What does God see when He looks at my heart?

This is Jesus’s standard, and it leads us to see how much we need Him. There is forgiveness and cleansing available, and He offers the strength to follow His commands in a way we never could on our own.