Summary
John Owen published The Mortification of Sin in 1656, and three and a half centuries later, no one has improved on it. Owen, the greatest theologian the Puritans produced, was not writing for seminarians or academics. He was writing for Christians who were losing the fight against sin and did not know why.
The book is based on a single verse: Romans 8:13. For if you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body, you will live. Owen takes that verse and builds the most thorough, most practical, and most psychologically penetrating treatment of sanctification in the English language.
Owen is not a perfectionist. He does not promise that you will ever be completely free of sin in this life. What he promises is war, a war you are equipped to win, battle by battle, through the power of the Holy Spirit. And he shows you exactly how to fight.
What Mortification Is, And What It Is Not
Owen begins by defining his terms with precision. To mortify sin means to weaken, starve, and progressively kill the power of indwelling sin in the believer's life. It does not mean sinless perfection. It does not mean the eradication of sinful desires. It means a daily, sustained campaign against the remaining corruption in your heart.
Owen insists on several crucial distinctions. Mortification is not the mere suppression of outward behavior. You can stop the external act of a sin while the desire still rages unchecked in your heart. That is not mortification. That is a dam waiting to break. True mortification attacks the root, not just the fruit.
Mortification is not achieved by willpower alone. Human resolution, however sincere, will always fail against indwelling sin. Owen knows this from experience and from Scripture. The flesh is too strong, too cunning, and too deeply embedded for mere determination to defeat it.
Mortification is not self-punishment. Fasting, vigils, and physical discipline have their place, but they cannot kill sin. Owen writes that a man may beat his body and starve his appetites and still be ruled by pride, bitterness, or lust in his heart. External mortification without internal transformation is theater, not warfare.
Mortification is not a private project. It is the work of the Holy Spirit through the believer. Owen returns to this point again and again: only the Spirit of God has the power to put sin to death. Your job is to cooperate with the Spirit, using the means the Spirit provides. But the power is His, not yours.
The Danger of Unmortified Sin
Owen's treatment of what happens when sin is left unchecked is among the most sobering passages in Christian literature. He warns that sin that is not actively mortified will grow. It never remains static. An unmortified lust will harden the conscience, darken the mind, weaken the will, and eventually bring the believer to a place where they can sin without feeling anything at all.
Owen compares unmortified sin to a disease that is ignored. At first, the symptoms are mild, an occasional temptation, a wandering thought, a small compromise. But left untreated, the disease spreads. It corrupts judgment so that you begin to rationalize. It weakens resistance so that you give in more quickly and with less guilt. It hardens the heart so that the things that once grieved you no longer bother you at all.
The progression Owen describes is chillingly recognizable. Temptation moves to contemplation. Contemplation moves to rationalization. Rationalization moves to action. Action moves to habit. Habit moves to slavery. And slavery moves to a seared conscience that can no longer distinguish between the voice of God and the voice of the flesh. Owen has watched this progression unfold in believers he knew. He writes with the urgency of a man who has seen friends and parishioners fall and does not want to see you fall next.
Owen also addresses the communal damage of unmortified sin. A believer who harbors secret sin does not sin in isolation. Their sin affects their family, their church, their witness, and their usefulness in the kingdom. Owen argues that one of the most loving things you can do for the people around you is to fight your own sin with relentless intensity.
The Rules of Engagement
The practical heart of the book is Owen's series of directions for how to mortify a particular sin. These are not abstract principles but battle-tested rules of engagement.
First, diagnose the specific sin. Owen insists that you cannot fight sin in general. You must identify the particular lust, the specific pattern, the exact point where you are most vulnerable. Vague spiritual warfare produces vague results. Name the enemy. Know the battlefield.
Second, load your conscience with the guilt and danger of the sin. This is not guilt for guilt's sake. It is the spiritual equivalent of a doctor showing you the X-ray of your tumor. You need to see clearly what this sin is doing to you, to your relationship with God, to your family, and to your ministry.
Third, long for deliverance. Owen says that a person who merely wishes to stop sinning is very different from a person who pants for deliverance the way a hunted deer pants for water. The degree of your longing measures the sincerity of your mortification.
Fourth, consider whether the sin is rooted in your natural temperament. Some people are more inclined to anger, others to lust, others to covetousness, others to pride. Know yourself. Your greatest vulnerability is the sin that flows most naturally from your constitution.
Fifth, attack the first movements of sin immediately. Do not give temptation time to make its case. Owen compares the first stirring of temptation to a small flame: easily extinguished when it starts, impossible to control once it has caught the timbers. Strike early and strike hard.
Sixth, meditate daily on the greatness, majesty, and holiness of God. Owen argues that a heart full of God has no room for sin. The expulsive power of a new affection, seeing God as more beautiful, more satisfying, more glorious than anything sin offers, is the deepest weapon in the believer's arsenal. You do not defeat lust by merely saying no. You defeat it by being captivated by something infinitely more beautiful.
Seventh, fill your mind with Scripture. The Word of God is the sword of the Spirit, and Owen insists that a believer who neglects Scripture is a soldier who has thrown away his weapon. Regular, sustained, prayerful engagement with the Bible is not optional in the war against sin.
Eighth, pray without ceasing. Bring the specific sin to God. Name it. Confess it. Ask for power to resist it. Owen says that prayerless mortification is a contradiction in terms. The Spirit mortifies sin in response to believing prayer.
The Role of the Holy Spirit
Owen never lets you forget that the power to mortify sin is not in you. It is in the Holy Spirit. Every direction he gives, every strategy he recommends, is a means through which the Spirit works. You cannot mortify sin by resolve, discipline, or technique alone. You must rely on the Spirit, and the Spirit has never failed to help a believer who sincerely and persistently asks.
This is what separates Owen's approach from every self-help book ever written. Self-help says you have the power within you. Owen says you do not. But the Spirit who raised Christ from the dead dwells in you, and His power is sufficient for every battle you will ever face.
Owen also connects mortification to the gospel. The blood of Christ is not only the ground of your forgiveness. It is the power of your sanctification. When Owen tells you to set faith at work on Christ for the killing of your sin, he means that the daily fight against sin must be fueled by a daily return to the cross. You do not fight sin by moving beyond the gospel. You fight sin by going deeper into it. The cross reminds you that sin has been defeated in principle and that the power that conquered death is available to conquer your besetting sin.
Owen develops the Spirit's role with theological depth. He explains that the Spirit mortifies sin by revealing the beauty of Christ, by applying the promises of the gospel to the conscience, by strengthening the new nature against the old, and by producing in the believer the fruit of love, joy, peace, patience, and self-control that displaces the works of the flesh. The Spirit does not work in a vacuum. He works through the means of grace: Scripture, prayer, sacraments, and the fellowship of the saints.
The Hope
Owen does not leave the reader in a perpetual state of war with no hope of victory. He promises real progress. Mortification works. Sin does weaken under sustained assault. The Spirit does produce change. The Christian who fights daily will find, not perfection, but growing freedom. Temptations that once overwhelmed will lose their grip. Patterns that once seemed unbreakable will crack. The heart that once ran toward sin will begin, slowly but truly, to run toward God.
The Mortification of Sin is not a comfortable book. It is the most honest, most demanding, and most hopeful treatment of the Christian's battle against sin that has ever been written. It has helped believers fight for three hundred and fifty years. It will help you fight today.