“Be Killing Sin”: The Biblical Call to Mortification

Second, Owen notes the persons whose duty it is: “If . . . you put to death . . .” Those in whom there is no condemnation (Rom. 8:1), those who are united by faith to Christ and are born again from above—you must “put to death the deeds of the body.” “The choicest believers,” Owen writes, “who are assuredly freed from the condemning power of sin, ought yet to make it their business all their days to mortify the indwelling power of sin.” None but Christians can mortify sin, and all who are truly Christians must mortify sin. When we get this wrong—and church history is full of examples of exactly this error—we fatally undermine the gospel. To teach the unconverted to kill their sin is to require that people deal with sin before coming to Christ. Not only is this to demand an impossibility (dead people cannot do anything, especially remove the cause of their own spiritual death), it is to put the sanctification-cart before the justification-horse. It makes acceptance with God dependent on our mortification of sin and not on the righteousness of Christ imputed to us and received by faith alone, worked into our hearts by the Holy Spirit, who has made us alive in Jesus. Sinners must come to Christ with their sin. They can come no other way. But having come, everyone in Christ must mortify his sin.

Third, Owen highlights the promise attached to the duty: “If . . . you put to death the deeds of the body, you will live.” Instead of the present spiritual death and future eternal death that sin’s mastery produces, a Christian whose sin is being mortified is promised “the joy, comfort, and vigor” of his new life in Christ as well as the fullness of life that is the believer’s reward in the world to come. While killing sin (and its corollary, walking in godly obedience) in no way entitles us to heaven—only the perfect obedience and blood of Christ can do that—the mortification of sin fits us for heaven. Jesus’ righteousness imputed to us and received by faith alone qualifies sinners for eternal life. But likeness to Jesus imparted to us and lived out in mortification and vivification makes us ready to dwell with Him forever. These two always go together. All who are alive in Christ kill their sin. Everyone alive forever in heavenly glory killed his sin on earth. And yet no one in heaven earned his place in glory by killing his sin. The citizens of heaven adore only the Lamb who was slain and take no credit for their presence around His throne.

Fourth, Owen points us to the means by which we are enabled to mortify sin: “If by the Spirit you put to death . . .” The Spirit has united us to Christ. He dwells in us. We are led by the Spirit. The Spirit gives us life. As the Spirit of our adoption, He bears witness with our spirits that we are children of God. He helps us in our weaknesses when we do not know what to pray for as we ought. He intercedes for us with groans too deep for words. It is by the ministry of this Spirit alone that sin can be put to death.

All other ways of mortification are vain, all helps leave us helpless; it must be done by the Spirit. . . . Mortification from a self-strength, carried on by ways of self-invention, unto the end of a self-righteousness, is the soul and substance of all false religion in the world.

Here is the balance of the biblical teaching on the mortification of sin. Here is the only way to avoid the poisons of morbid introspection, self-reliant triumphalism, or passive quietism. If we emphasize only the duty of mortification, we might become self-righteous, believing that we have all the power we need in ourselves to do it. Just as likely, we may become defeated and despairing, believing that while this is indeed our duty, we are nonetheless doomed to failure because our capacity to kill our sin seems so very feeble. On the other hand, if we emphasize only the Spirit’s agency in the mortification of our sin, we might become passive, thinking that we have nothing to do but “let go and let God,” who will, in a moment of serene surrender on our part, painlessly “zap” the cancer of our sin away. But the scriptural teaching calls us to rely on the supplies of the Spirit of Christ for power and strength and to seize the duty to put our sin to death with alacrity and determination, expending all our power and strength to do it. As Paul tells the Philippians, we as Christians are to “work out [our] own salvation with fear and trembling, for it is God who works in [us], both to will and to work for his good pleasure” (Phil. 2:12–13). We work, we strive, we kill sin, but we do it while always looking not to our own resources but to Christ, who gives us His Spirit. In this way, we will not grow weary or give up. We will not boast or take the credit. We will not coast and fail to do our duty.

Finally, Owen points out the conditionality of the clause in Romans 8:13: “If by the Spirit you put to death the deeds of the body . . .” The condition highlights the urgency and necessity of the duty enjoined. As we’ve already pointed out, this duty is not a causal necessity. Our salvation is not caused by our mortification of sin or by any other work of ours. The cause of our salvation is Christ’s obedience and blood alone. But while the duty of killing sin is not the necessary cause of eternal life, it is the necessary means by which we come to eternal life. Life grows in us as sin dies in us. This is the great motive to prompt us on in what is a painful work.

Consider again the image of mortification, of killing sin. It is a crucifixion, a dreadful, lingering death. Recall how even the sinless Savior, in His perfect humanity, agonized over the horror of the cross, and we will quickly understand how our wicked flesh shrinks back from the prospect of its own destruction. This is why, as every Christian has discovered in trying to put his sin to death, indwelling sin will do anything, strike any bargain, make any promise, if only we will let it live. It will curtail its activities for a season and make it seem as if we no longer need to worry about it, if only we will not take radical action to put it to death. It will seek to persuade us that we are being immoderate and overly scrupulous in seeking its complete destruction. “After all, reasonable people allow room for indulgence from time to time,” it tells us. Sin will point out how odd its death in our lives will make us appear in the eyes of our unconverted friends and neighbors. “But if you let me live, I can help you fit right in,” it says. And by a thousand other enticements or threats, our sin pleads and argues and intimidates us into taking almost any other course than the course of Christian duty: the mortification of our sin. The flesh dies slowly. It hurts to kill sin. We love our vices, and it wounds us to kill our darlings. But die they must if we are to live.

But, Paul says, if we put to death the deeds done in the body, whatever the lies sin may whisper to the contrary, the painful process of mortification will give place to life, and life in all its abundance (John 10:10). Life with Christ, with every spiritual grace ripening on the vine of your life, a life well pleasing to God, enjoying His favor and filled with His Spirit: This is the blessing that God has bound Himself to give you, if you obey His command. “If by the Spirit you put to death the deeds of the body, you will live.”

So Owen states, “Do you mortify; do you make it your daily work; be always at it whilst you live; cease not a day from this work; be killing sin or it will be killing you.”