Five hundred years ago, the church stood in urgent need of reform. Shallow teaching, spiritual weakness, and an overemphasis on outward performance had hollowed out Christian life. According to Martin Luther, the problem ran deeper than corruption or poor practice. At its core was a failure to understand the human heart.

That conviction lay at the centre of the Reformation and remains just as pressing today. If lives are to be truly transformed, and if the church is to be genuinely renewed, then the heart must be addressed.

The limits of behavioural righteousness
Luther’s early formation was shaped by Aristotle’s ethics, which taught that people become righteous through repeated righteous actions. This view dominated theological education in his day, and Luther pursued it with intensity through fasting, prayer, confession, and religious observance. Yet peace remained elusive. Righteousness always appeared just beyond reach, producing exhaustion rather than joy and shaping an image of God as demanding rather than gracious. Through this struggle, Luther came to see that behaviour could restrain action but could not form love for God. Righteous deeds flow from a righteous heart; they do not create it.

Grace and changed desire
At the centre of this shift was a deeper understanding of grace. Grace is not divine assistance that helps people try harder. It is the power of God that changes what pleases us. When grace takes hold, obedience flows from delight.

This is the work of the Holy Spirit. While human effort can reach only as far as outward behaviour, the Spirit works at a deeper level, reshaping the loves and longings of the heart. True righteousness is produced when the heart begins to love what God loves.

The slavery of the will
This understanding of the heart brought Luther into sharp disagreement with Erasmus, the leading scholar of the day. Erasmus believed the church needed reform, but he viewed human sinfulness as relatively shallow. People, he argued, were morally weak but capable. With encouragement and effort, they could choose what was right.

Luther saw the problem differently. Human beings do make choices, but those choices are always driven by desire. People freely choose what they want, but they do not freely choose what they want to want. The will follows the heart. This is what Luther meant by the slavery of the will. The will is not coerced, but governed by affection. Sin arises because the heart desires 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” (James 1:14–15). Left to themselves, people do not merely struggle to choose God. Their hearts are inclined elsewhere.

Moralism and its effects
These theological differences produced radically different visions of Christian life. For Erasmus, the church functioned like an army. Christians were soldiers who needed rules, and pastors were responsible for enforcing discipline. Failure was met with frustration, because obedience was assumed to be achievable.

When behaviour becomes the primary focus, hypocrisy flourishes. People learn to manage appearances while desires remain unchanged. Moralism produces either pride or despair, but never lasting transformation.

Luther, by contrast, understood the church as a family. The central issue was not rule-keeping, but relationship. Sin was a preference for something other than God. Obedience, therefore, could not be produced by command alone. The heart had to be won.

Intellectualism and the neglect of the heart
A different but equally damaging error emerged later, particularly in reaction against moralism. Some reduced faith to intellectual agreement, defining it as merely acknowledging the truth of the gospel. As a result, this approach produced preaching that prioritised explanation without persuasion. Sermons became lectures. The text was analysed accurately, but the heart was never addressed. While doctrinal precision was maintained, love for Christ was often absent.

Yet Scripture makes clear that faith involves more than knowledge. Even demons possess correct theology. Saving faith is an act of the heart as well as the mind. It is trust, rest, and delight in Christ. People do not fail to believe merely because they lack information. They fail to believe because they do not love the truth.

How hearts truly change
Hearts cannot be changed by willpower. Sinful desires cannot simply be removed; they must be displaced. The heart will always love something. Attempting to expel sin without replacing it leaves the heart unchanged.

True change occurs only when a greater affection takes hold. As the goodness and beauty of Christ are proclaimed, the Spirit awakens new desires. Love for God grows stronger than love for sin, and obedience flows naturally from joy.

This is why the gospel must always be more than instruction or exhortation. It must present Christ himself as worthy of love and trust. Only then can deep and lasting transformation take place.

When the heart is misunderstood, Christianity collapses into either moral effort or intellectual assent. Both leave people enslaved, either to performance or to pride. The gospel addresses a deeper problem: disordered love.

By the work of the Holy Spirit, hearts are renewed to delight in God. From that renewal flows obedience, freedom, and joy. True reform, in the church and in individual lives, begins not with behaviour or knowledge, but with the heart.