Spurgeon opens with the observation that wholeheartedness is the universal law of success — in business, science, medicine, and law alike — and argues it is no less true in religion, illustrating this by pointing to how Islam spread by the sword-swinging zeal of its earliest followers and how Francis Xavier carried Roman Catholicism to India, Burma, China, and Japan through sheer burning energy, before pressing the question: if false religions have conquered the world through earnestness, what excuse does the true church have for its lukewarm half-heartedness? He then traces what whole-heartedness actually looks like in the life of a believer: it fills the mind constantly with Christ's cause rather than occasional fits of enthusiasm; it turns vague resolutions into definite, immovable purposes that cannot be shaken by opposition or failure; it shows itself in persevering effort — running when possible, walking when necessary, crawling when that is all that remains — and it drives the believer to fervent, wrestling, take-no-denial prayer as the source of all strength. He closes with a double appeal — urging the church not to squander the extraordinary mercy God has shown in pouring conversions upon them, since a congregation so favored will be held to a proportionally severe account if it sleeps; and turning to the unconverted with a warning that if they find religion unserious now, they will find death, judgment, and eternity to be in deadly earnest, while Christ's agony in the garden and blood at the cross are proof that heaven did not trifle over their souls — and he calls every careless hearer to trust Christ now with all the heart, since that is the only "earnestness" God requires of the sinner who has no goodness to offer but a willing surrender.
Sermon delivered by Charles Spurgeon on March 9, 1862.