The Unsearchable Heart and the All-Searching God Text: Jeremiah 17:9-10
Introduction: The Diagnostic Center of the Universe
We live in an age of profound self-deception. Our entire culture is built on the sandy foundation of a single, damnable lie: "Follow your heart." We are told from every quarter, from the movies we watch to the songs we hear to the pabulum served up in our schools, that the heart is a trustworthy guide, a pristine compass pointing to the true north of our personal happiness. We are told to look within, to trust our feelings, to be true to ourselves. This is the central dogma of our secular religion, and it is a straight shot of poison.
The prophet Jeremiah, speaking for the living God, comes into this modern marketplace of ideas like a wrecking ball. He does not offer a gentle critique or a minor course correction. He takes the central idol of our age, the deified human heart, and smashes it to pieces on the floor. He tells us that the very thing we are told to trust is, in fact, the most untrustworthy thing in the universe. It is not just a little off; it is deceitful above all things. It is not just feeling a bit under the weather; it is desperately sick.
This is not a popular message. It is offensive. It cuts against the grain of every natural inclination we have. We want to believe we are basically good, that our intentions are pure, and that our problems are external to us. But the Bible insists that the problem is not "out there." The problem is in here. The problem is the human heart. And until we are prepared to accept God's diagnosis of our condition, we will never, ever seek out the only physician who can provide the cure.
These two verses in Jeremiah are the divine MRI scan of the human soul. They give us the bad news first, in all its unvarnished severity. But they do not leave us there. They immediately point us to the one who is not deceived, the one who knows us better than we know ourselves, and the one whose searching gaze is the beginning of all true wisdom and all true healing. This is the foundation of the doctrine of sin, which is itself the foundation for the glorious doctrine of salvation.
The Text
"The heart is more deceitful than all else And is desperately sick; Who can know it? I, Yahweh, search the heart; I test the inmost being, Even to give to each man according to his ways, According to the fruit of his deeds."
(Jeremiah 17:9-10 LSB)
The Treacherous Heart (v. 9)
We begin with God's unflinching diagnosis of the human condition apart from grace.
"The heart is more deceitful than all else And is desperately sick; Who can know it?" (Jeremiah 17:9)
The "heart" in Scripture is not a reference to our sentimental emotions. It is the command center of the entire person. It is the seat of the intellect, the will, and the affections. It is the source code of our lives. And God's verdict on this command center is that it is fundamentally treacherous. The Hebrew word for deceitful here, `aqob`, carries the idea of being crooked, slippery, a supplanter. It is the root of Jacob's name, given to him because he came out of the womb grabbing his brother's heel. The unregenerate human heart is a born conniver, a natural-born grifter.
And notice the superlative: it is more deceitful than "all else." More deceitful than a con man's smile, more deceitful than a politician's promise, more deceitful than the serpent in the garden. And who is its primary victim? We are. The heart's greatest deception is self-deception. We are masters at manufacturing excuses, justifications, and noble-sounding motives for our own sin. We curate a vision of ourselves as the noble protagonist in our own story, when in reality, we are the villain. We think we want justice, but we really want revenge. We think we are pursuing truth, but we are really just protecting our pride. The heart is a brilliant lawyer, capable of arguing that black is white and up is down, and its only client is the self.
Not only is it deceitful, but it is "desperately sick." The word here means incurable by human means. It is terminally ill. This is what the theologians call total depravity. This does not mean that every unbeliever is as wicked as he could possibly be in his behavior. A man may be a respectable pagan, a good neighbor, and a loving father. But it does mean that sin has corrupted every part of his being. His mind is darkened, his will is in bondage, and his affections are disordered. There is no island of pristine goodness within him that can rise up and save him. The sickness has infected the whole man. Like a drop of ink in a glass of water, the whole has been colored by the fall.
The verse ends with a rhetorical question that drives the point home: "Who can know it?" The answer, of course, is that no mere man can. We cannot plumb the depths of our own corruption. We are constantly surprised by the sin that erupts from us. We make resolutions and break them. We set goals and fail to meet them. We are a mystery to ourselves. We are like a man trying to get a clear look at his own eyeball. We are too close to the subject, and the instrument we are using for the examination is the very thing that is diseased.
The Divine Cardiologist (v. 10)
The despair of verse 9 is immediately met by the declaration of verse 10. Man cannot know his own heart, but that is not the end of the story.
"I, Yahweh, search the heart; I test the inmost being, Even to give to each man according to his ways, According to the fruit of his deeds." (Jeremiah 17:10)
Here God answers the rhetorical question. "Who can know it?" "I can." The Lord, Yahweh, the covenant God of Israel, declares His unique prerogative. He alone is the divine cardiologist. The word "search" here is not a casual glance. It is a deep, penetrating, exhaustive examination. He tests the "inmost being," literally the kidneys, which the Hebrews regarded as the seat of the deepest affections and conscience. Nothing is hidden from Him. Our carefully constructed facades, our secret motives, our hidden sins, are all an open book to Him. He sees past the performance to the performer.
This should be terrifying news to the unrepentant. There is no corner of your soul where you can hide from God. He knows why you really did what you did. He knows the pride lurking behind your false humility. He knows the lust behind your flattering words. He knows the bitterness you are nursing in the dark. And this searching is not for the purpose of idle curiosity. It is for the purpose of judgment.
He searches in order "to give to each man according to his ways, According to the fruit of his deeds." This is the unbending principle of divine justice. God is not mocked; whatsoever a man sows, that shall he also reap. The "ways" are the paths we choose, the direction of our lives. The "fruit" is the inevitable result of the tree we are. A bad tree cannot produce good fruit. The deeds of a deceitful and desperately sick heart will always, ultimately, be sinful deeds, and they will be judged accordingly.
This is where the law brings us to our knees. If our hearts are incurably sick, and if God judges us based on the fruit that comes from those hearts, then we are all undone. We are all guilty. We all stand condemned before the perfect, all-knowing Judge. There is no hope for us if this is the final word. But thanks be to God, it is not.
The Gospel Transplant
This passage, like all of Scripture, points us to our desperate need for a savior. The diagnosis of Jeremiah 17 is the reason we need the gospel. If the heart is the problem, then the solution must be a new heart.
And this is precisely what God promises in the new covenant. Through another prophet, God says, "And I will give you a new heart, and a new spirit I will put within you. And I will remove the heart of stone from your flesh and give you a heart of flesh" (Ezekiel 36:26). This is the miracle of regeneration. This is the divine heart transplant that is the sole property of God the Holy Spirit.
When God saves a man, He does not simply polish up the old, deceitful heart. He does not give it a coat of moral paint. He rips out the diseased, cancerous organ and replaces it with a new one. He gives us a heart that loves Him, that desires His law, and that is capable of producing good fruit for the first time.
How is this possible? Because the judgment we deserved fell upon another. God searched the heart of His own Son, Jesus Christ, and found no deceit, no sickness, no sin. He was the only man with a perfectly pure heart. And on the cross, God treated Him as though He had our deceitful heart, so that in Him, we might be given His righteous heart. He received the wages for our deeds, so that we might receive the reward for His.
For the Christian, then, the searching gaze of God in Jeremiah 17:10 is no longer a terror, but a comfort. We can now pray with the psalmist, "Search me, O God, and know my heart! Try me and know my thoughts! And see if there be any grievous way in me, and lead me in the way everlasting!" (Psalm 139:23-24). We invite the divine surgeon to continue His work in us. We know that remnants of the old sickness remain, that the deceitfulness still tries to assert itself. But we now have a new heart, a new nature, and the Spirit of God within us to fight that battle. And because He continues to search us, He continues to cleanse us. He exposes the remaining corruption so that He might kill it, and He does this to bring forth the fruit of righteousness in us, not for our justification, but as the evidence of it. Our good works are the fruit that proves the tree has been made new.
So do not trust your heart. Trust the God who knows your heart. Despair of your own ability to fix yourself, and run to the only physician who can perform the transplant you so desperately need. Run to Christ.