IS JEREMIAH 17:9 STILL TRUE FOR CHRISTIANS?

Picture this: A mature believer, respected in church, suddenly explodes in anger at his spouse over something trivial. In the aftermath, he discovers layers of resentment he didn’t even know existed. “Where did that come from?” he wonders, genuinely shocked by what emerged from his own heart.

This scenario plays out in Christian homes everywhere, leaving believers wrestling with an uncomfortable question: If we have new hearts in Christ, why do we still surprise ourselves with our capacity for sin? Popular Christian culture encourages us to “follow our hearts” and “trust what God has placed in your heart.” But does this align with biblical wisdom?

The prophet Jeremiah declared “the heart is deceitful above all things, and desperately sick; who can understand it?” (Jeremiah 17:9). While Christians receive genuine transformation through regeneration, the ongoing presence of sin means this ancient warning remains practically relevant for believers today. We need continued vigilance and dependence on Scripture rather than subjective feelings to navigate the Christian life wisely.

 

THE VERSE IN CONTEXT

Jeremiah spoke these sobering words to expose why God’s people kept falling into spiritual disaster. Let’s unpack what makes this verse so penetrating:

“Deceitful above all things”: The Hebrew word aqob means “crooked” or “insidious”—like Jacob grabbing his brother’s heel to gain advantage. Our hearts don’t just make mistakes; they actively mislead us. They present our selfish desires as noble motives and our fears as spiritual wisdom. The heart excels at making wrong choices feel completely right.

“Desperately sick”: The Hebrew anash describes something incurably diseased, morally terminal apart from divine intervention. This isn’t about occasional bad days or personality quirks. Jeremiah is diagnosing a fundamental corruption in the very centre of human decision-making and desire.

“Who can understand it?”: We ourselves cannot fully grasp our own hearts’ capacity for self-deception. What’s worse, we’re often the last to see our own blind spots, pride, and mixed motives. What feels like spiritual discernment might be rationalised preference; what seems like righteous anger might be wounded pride in disguise.

Universal scope: This describes the natural human condition before God—not just “really bad people,” but all of us. The heart as the seat of will, emotion, and moral choice has been fundamentally compromised by the fall.

 

THE PROMISED NEW HEART: REAL TRANSFORMATION

God doesn’t leave us in this desperate condition. Through regeneration, He creates genuine spiritual transformation that changes everything. Scripture promises believers will receive a new heart (Ezekiel 36:26), become new creations (2 Corinthians 5:17), and be made spiritually alive (Ephesians 2:1-5).

This transformation is real and profound. The Reformed tradition rightly emphasizes that regeneration creates authentic change in a believer’s fundamental orientation. Where once we were “only evil continually,” we now possess genuine capacity to love God, hunger for righteousness, and respond to His Word. The Holy Spirit indwells us, creating new desires and spiritual discernment that were impossible in our natural state.

We see evidence of this new heart throughout Scripture and Christian experience. Believers demonstrate love for God and His people (1 John), hunger for righteousness (Matthew 5:6), and spiritual understanding that unbelievers cannot grasp (1 Corinthians 2:14-16). The transformation is so real that we can have confidence in our salvation and growth in holiness.

 

THE CONTINUING STRUGGLE: WHY HEARTS STILL DECEIVE

Despite this glorious reality, Scripture and experience teach us that regeneration doesn’t eliminate our capacity for self-deception. Reformed theology captures this tension in the Latin phrase simul justus et peccator—we’re simultaneously justified and still struggling with sin.

Ongoing sin’s reality: The apostle Paul, writing as a mature believer, described his continued battle: “I do not do the good I want, but the evil I do not want is what I keep on doing” (Romans 7:19). If Paul struggled with sin’s ongoing presence, we should expect the same. Our hearts retain capacity to mislead us about our motives, spiritual condition, and even God’s will for our lives.

Self-deception remains active: John warns believers: “If we say we have no sin, we deceive ourselves, and the truth is not in us” (1 John 1:8). Notice he’s writing to Christians, not unbelievers. Even regenerate hearts can convince us we’re more spiritual, more loving, or more mature than we actually are. Pride often masquerades as confidence; fear disguises itself as prudence; selfish ambition clothes itself in spiritual language.

Biblical examples abound: Peter confidently declared he’d never deny Jesus, genuinely believing his own heart’s testimony (Matthew 26:33-35). The disciples argued about greatness even after years with Christ (Luke 22:24). These weren’t hypocrites but sincere believers whose hearts misled them about their own spiritual state and motives.

We can’t trust our feelings: Scripture consistently warns against trusting our feelings over God’s revealed truth. Jeremiah himself wrote, “Cursed is the man who trusts in man and makes flesh his strength” (17:5)—including trusting our own emotional assessment of situations. What feels right in the moment may contradict God’s wisdom; what seems like spiritual leading may well be wishful thinking. Or raw unprocessed emotion.

 

LIVING WITH GOSPEL WISDOM

How then should Christians live with this tension? We need biblical wisdom that acknowledges both our new hearts and their remaining capacity for self-deception.

1. Scripture, not subjective feelings, must be our primary authority. God’s Word is “living and active, sharper than any two-edged sword, piercing to the division of soul and of spirit” (Hebrews 4:12). When our hearts conflict with Scripture, Scripture wins. When we’re unsure about motives or direction, we test our impulses against biblical truth rather than simply trusting our feelings.
2. We need regular heart examination through God’s Word. The Psalmist prayed, “Search me, O God, and know my heart! Try me and know my thoughts!” (Psalm 139:23-24). We should regularly ask the Spirit to illuminate our hearts through Scripture, revealing blind spots, mixed motives, and areas needing growth.
3. Christian community provides essential accountability. Fellow believers can often see what we cannot see in ourselves (Galatians 6:1). Wise friends, pastors, and mentors help expose our self-deceptions with gentle truthfulness.
4. We find our assurance in Christ’s work, not our heart’s testimony. John reminds us “whenever our heart condemns us, God is greater than our heart, and he knows everything” (1 John 3:20). When our hearts falsely accuse or falsely assure, we rest in the gospel’s objective truth.

 

BALANCED BIBLICAL REALISM

Christians do possess new hearts that genuinely love God and hunger for righteousness. This transformation is real, permanent, and grows throughout our lives. But these renewed hearts retain capacity for self-deception until we receive glorified bodies at Christ’s return.

This reality calls us to humble dependence on Scripture over feelings, community wisdom over isolated decision-making, and the Spirit’s illumination over our own understanding. We can have confidence in our salvation while maintaining healthy suspicion of our motives. We can trust God’s promises while questioning our own emotional assessments.

Jeremiah 17:9 doesn’t negate the new covenant’s promises—it keeps us grounded in gospel humility until that day when we see Him face to face and our transformation is complete.

 

THE CHRISTIAN HEART: STILL DESPERATELY WICKED? RELATED FAQs

Did John Calvin believe Christians still have desperately wicked hearts? Calvin distinguished between the “old man” and “new man” in believers: he taught both coexist until glorification. In his Institutes, he argued that while regeneration creates genuine spiritual life, “the remains of sin always abide in the regenerate”. Believers must “wage lifelong war” against indwelling corruption. Calvin emphasised Christians possess renewed hearts that truly love God, but these hearts retain “relics of sin” that can deceive us about our motives and spiritual condition.

• What about Jeremiah 24:7 and Ezekiel 11:19—don’t these promise completely new hearts? These passages do promise genuine heart transformation, but Reformed scholars interpret them as describing progressive rather than instantaneous perfection. John Murray argued the “heart of flesh” replaces the “heart of stone” in terms of fundamental orientation and capacity, not immediate moral perfection. The new heart has new desires and abilities—it can love God, respond to Scripture, and grow in holiness—but it coexists with remaining corruption until our resurrection.
• How do we distinguish between the Spirit’s leading and heart deception? Reformed theologian JI Packer wrote the Spirit always leads in accordance with Scripture, never contradicting God’s written Word. Genuine spiritual leading produces fruit consistent with biblical character (Galatians 5:22-23) and aligns with Scripture’s moral teachings. Heart deception, by contrast, often rationalizes behavior that conflicts with biblical wisdom or produces anxiety rather than the peace that marks Spirit-led decisions. When in doubt, Reformed practice emphasises testing impressions against Scripture and seeking wise counsel.
• Does this mean Christians can’t trust any of their feelings or desires? Reformed theology distinguishes between trusting feelings as ultimate authority versus recognising them as part of our renewed nature. Martyn Lloyd-Jones taught regenerate desires—like hunger for God’s Word, love for fellow believers, and longing for holiness—reflect genuine spiritual transformation. However, even these good desires can become mixed with pride, self-interest, or impatience. The key is subjecting all feelings and desires to Scripture’s authority while recognizing that God often works through sanctified emotions and renewed affections.
• How does Romans 8:16 fit—doesn’t the Spirit bear witness with our spirit? Reformed scholars like John Stott interpreted Romans 8:16 as the Spirit confirming our adoption through objective evidences of grace (love for God, hunger for righteousness, genuine repentance) rather than through subjective feelings alone. The Spirit’s witness comes primarily through illuminating Scripture’s promises and showing us Christ’s work, not through emotional experiences divorced from biblical truth. This witness can involve feelings of assurance, but it’s grounded in the objective reality of the gospel rather than in our subjective emotional states.

What practical advice did Puritan writers give for examining heart motives? Puritan authors like Richard Baxter and John Owen developed detailed methods for heart examination, emphasising regular self-reflection through Scripture and prayer. Owen advised believers to “be killing sin or it will be killing you,” advocating daily examination of motives, desires, and reactions against biblical standards. Baxter recommended keeping spiritual journals, regularly confessing discovered sins, and seeking accountability from mature believers. They taught healthy suspicion of our own hearts, combined with confidence in Christ’s righteousness, leads to both humility and assurance in the Christian life.

 

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