Where Preaching Gets Its Power

What makes a sermon unforgettable? What gives preaching real power?

For many, preaching is defined by eloquence, theological precision, or a well-structured outline. But as history and Scripture attest, something far deeper and more spiritual is at work when God’s Word is truly preached. That “something” is on full display in one of the most enduring sermons of the last two centuries: “The Expulsive Power of a New Affection,” preached in 1819 by Thomas Chalmers.

Though preached over two hundred years ago in a thick Scottish accent by a man reading from a manuscript, the sermon still resonates today. Why? Because it unveils a timeless truth: no amount of effort or discipline can rid the heart of sin unless a greater love takes its place.

This is the power of true preaching not merely informing minds, but transforming hearts.

A Man Transformed

Thomas Chalmers (1780–1847) was no ordinary preacher. Before becoming one of Scotland’s most celebrated ministers, he was a stranger to the gospel he later proclaimed with such passion. Early in his ministry, he treated his pastoral duties as secondary claiming two days a week was sufficient to fulfill the call of ministry.

But that changed. Through illness, the writings of men like William Wilberforce and Thomas Scott, and above all, the sovereign grace of God, Chalmers came face to face with his sin and the glorious sufficiency of Christ. That encounter didn’t just change his theology it changed his preaching.

He would go on to inspire men like Robert Murray M‘Cheyne, build over 200 churches in seven years, and lead Scotland’s evangelical movement into the formation of the Free Church of Scotland. Yet his most enduring legacy may be a single sermon.

The Sermon That Still Speaks

“The Expulsive Power of a New Affection” is anchored in 1 John 2:15:
“Do not love the world or the things in the world. If anyone loves the world, the love of the Father is not in him.”

Many modern sermons would unpack that verse with detailed exegesis and historical background. But Chalmers, while not ignoring the text, aimed deeper. He sought not just to explain the words, but to unleash their weight to let the truth burrow into the soul until it dislodged lesser loves.

His thesis is stunning in its simplicity: you can’t break sin’s grip merely by trying harder it must be replaced by a greater affection. A new love must drive out the old. The gospel doesn’t merely tell us to stop loving the world; it fills our hearts with something infinitely more satisfying: the love of the Father.

This is what gives preaching its power not tips for moral improvement, but a vision of the beauty and supremacy of Christ that awakens our hearts and reshapes our desires.

More Than Explanation

Chalmers’s preaching was not just expository; it was expositional in its fullest sense. He didn’t just define terms he unveiled glory. He didn’t merely convey ideas he confronted affections. As the Westminster Directory for Public Worship puts it, powerful preaching causes hearers to feel that “the word of God [is] quick and powerful, and a discerner of the thoughts and intents of the heart.”

In his commentary on Hebrews 2:11, John Calvin captured the same reality: “We ought not so much to consider men as speaking to us, as Christ by his own mouth.”

True preaching, then, is not simply man’s speech about God. It is Christ’s own voice, through the Spirit, piercing hearts with truth. And when that happens when the gospel is not only heard but felt sin begins to lose its grip.

The Heart Behind the Power

What made Chalmers so effective wasn’t eloquence (though he had it) or theological education (which he also had in abundance). It was that his own heart had been conquered. He knew firsthand what it meant to be overthrown by divine affection.

His own words capture it well: “With the tidings of the gospel in commission, [the preacher] may wield the only engine that can extirpate [worldly desires]… He has a truth in his possession which, into whatever heart it enters, will, like the rod of Aaron, swallow up them all.”

Chalmers knew that transformation doesn’t come by sheer willpower. No one is argued out of sin. They are wooed away by something more beautiful, more worthy, more enduring. Only a glimpse of the crucified and risen Christ can produce the new affection that expels the old.

Why This Still Matters

In a world of self-help and therapeutic religion, Chalmers’s message is a needed rebuke and a welcome balm. The church doesn’t need more moralistic messages or clever outlines. It needs preaching that awakens the soul sermons that lift Christ high enough for hearts to adore him.

A 2022 Barna study found that 44% of churchgoers struggle to stay engaged during sermons. But what if the issue isn’t attention spans, but affections? What if the solution isn’t shorter sermons, but truer ones ones that aim not only to explain the Bible but to exalt Christ?

This is why “The Expulsive Power of a New Affection” endures. It’s not a call to try harder it’s an invitation to behold Jesus. And in beholding him, to become new.

So, if your affections feel stale, if sin’s grip seems strong, if preaching feels flat, do what Augustine once did: tolle lege take up and read. Read Chalmers’s sermon. Let its truth soak in. Let it show you how much greater the love of God is than anything this world offers.

And if you’re a preacher, let it remind you of your aim: not merely to inform minds, but to ignite hearts.

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