Mortify therefore your members which are upon the earth; fornication, uncleanness, inordinate affection, evil concupiscence, and covetousness, which is idolatry: For which things’ sake the wrath of God cometh on the children of disobedience: In the which ye also walked some time, when ye lived in them.
— Colossians 3:5-7
Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin.
— Romans 6:6
Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God.
— Romans 6:13
Repent therefore of this thy wickedness, and pray God, if perhaps the thought of thine heart may be forgiven thee.
— Acts 8:22
The Principal Assertion Concerning the Necessity of Mortification Proposed, by John Owen. The following contains Chapter Two of his work, “Of the Mortification of Sin in Believers”—Abridged and Simplified.
For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live.
— Romans 8:13
1. The Ongoing Battle Against Sin
Even the most mature believers—those assured of their salvation—must continually mortify sin. The Apostle Paul exhorts Christians, “Put to death therefore what is earthly in you” (Col. 3:5). He was writing to those already united with Christ in His death and resurrection. Yet, they were still commanded to actively put sin to death. This is not an occasional duty but a lifelong battle. If we do not actively kill sin, it will seek to kill us.
Jesus teaches that His Father prunes every fruitful branch so that it may bear more fruit (John 15:2). This pruning is ongoing. Paul, too, testifies to his constant battle against sin: “I discipline my body and keep it under control” (1 Cor. 9:27). If such a man, who had been greatly used by God, devoted himself daily to mortification, how can we think we are exempt?
2. Sin Remains in Every Believer
Sin remains within us as long as we live in this world. Some claim to have attained perfection, yet such views are self-deceptive. Scripture warns that we will struggle with sin throughout our lives. Paul himself confessed, “Not that I have already obtained this or am already perfect” (Phil. 3:12). We must be continually renewed, for “our inner self is being renewed day by day” (2 Cor. 4:16).
The flesh still opposes the Spirit (Gal. 5:17). Darkness remains in our understanding, and our obedience is imperfect. We carry within us “a body of death” (Rom. 7:24), from which we will not be fully freed until our physical death and resurrection in glory (Phil. 3:21). Therefore, mortifying sin is not optional—it is a necessary and ongoing duty.
3. Sin Is Always Active
Sin does not simply reside in us—it constantly seeks to act. It never rests. When it appears quiet, it is often working most subtly. It tempts, entices, and corrupts. Paul describes this ongoing struggle: “Ido not do the good I want, but the evil I do not want is what I keep on doing” (Rom. 7:19). Even when we desire to do good, sin opposes us.
If sin is always at work, then we must be constantly engaged in its mortification. If we are idle, we will be overcome. Sin aims to control us, and if left unchecked, it will bring forth greater and greater iniquity (Gal. 5:19-21). Every sin, if not resisted, seeks to grow into its most extreme form—anger into murder, lust into adultery, unbelief into apostasy. Sin has no limit but total rebellion against God.
4. The Spirit Enables Mortification
The Holy Spirit is given to us so that we may overcome sin. The flesh and the Spirit oppose each other (Gal. 5:17), but it is by the Spirit that we put to death the deeds of the flesh (Rom. 8:13). If we neglect this work, we disregard the very purpose of the Spirit’s presence in our lives.
It would be foolish to neglect the help that God has provided. If we do not engage in this battle, sin will gain strength, and our spiritual life will weaken. Neglecting to mortify sin dishonors God’s grace and invites spiritual decline.
5. The Danger of Neglecting Mortification
Failing to mortify sin leads to serious consequences. Over time, sin gains strength and hardens the heart. It leads to backsliding and, in some cases, apostasy. Many who once showed signs of faith have abandoned the truth because they failed to battle sin daily.
Sin does not merely persist—it seeks to dominate. If left unchecked, it will corrupt our thoughts, desires, and actions. It will diminish our love for God, weaken our zeal, and hinder our prayers. Those who neglect mortification may find themselves spiritually cold, entangled in sin, and far from God.
Neglecting this duty also affects others. Hypocritical and lukewarm Christians cause others to stumble. Unmortified sin in a professing believer’s life can discourage weaker Christians and provide an excuse for the ungodly to remain in sin. A person may claim to be a Christian, but if their life is marked by pride, worldliness, selfishness, or strife, they bring dishonor to the gospel.
6. The Call to Continual Growth
We are called to “perfect holiness in the fear of God” (2 Cor. 7:1) and to “grow in the grace and knowledge of our Lord Jesus Christ” (2 Pet. 3:18). This requires daily mortification of sin. Sin resists every effort to grow in holiness. If we are not actively resisting sin, we are not making progress in sanctification.
True Christian growth is marked by continual battle against sin. If we are content to let sin live, we deceive ourselves. Every step forward in holiness is taken over the defeated remnants of sin. We must always be putting sin to death.
Conclusion
The cross of Christ has already secured the ultimate defeat of sin, yet sin remains in us and must be mortified daily. The work of mortification is not optional—it is essential for every believer. If we fail to fight, sin will gain strength. If we engage in battle, the Spirit will empower us. This is a lifelong duty, but one that leads to greater joy, peace, and assurance in Christ.
Let us, then, take up this work with diligence, remembering that “ifby the Spirit you put to death the deeds of the body, you will live”(Rom. 8:13).
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