The definitive treatment on killing sin is a series of sermons John Owen preached on Romans 8:13 that eventually became Of the Mortification of Sin in Believers (1656). In the book, Owen has several pithy statements of advice on killing sin.
“Be killing sin or it will be killing you”
According to Romans 8:13, Christians are to actively kill sin in their lives. The reason is simple: sin is serious. If we do not kill sin, it will kill us! As Paul states, “if you are living according to the flesh, you must die.” Killing sin is a serious matter—a life and death matter. Sin is like cancer. If cancer is not “killed,” it will kill you.
“When sin lets us alone we may let sin alone”
The implication is that sin never leaves us alone and so we must not leave it alone. This is because sin is active. Paul implies as much when he writes to “brethren” to “put to death the deeds of the body” (Romans 8:12-13). Stated another way, sin is never neutral, even for the Christian. Sin is not entirely gone. Yes, the power of sin is broken; sin is in prison. But sin tries to regain its reign. And as such, sin will not shrivel up, grow weak and inactive, and die of old age. Sin is like a tree. If we do not chop it down and root it up, the older it gets, the stronger and deeper the roots and branches become.
“There is no death of sin without the death of Christ”
Though sin never leaves us alone, we are never alone. Through the indwelling Spirit, we have the power to kill indwelling sin, because sin is defeated in the death of Christ. As Paul states, we must not live according to the flesh, but can and must, through the Spirit’s power, put to death the sin in our lives that has been ultimately defeated by Christ (Romans 8:13). The only sin you will ever kill is the sin you recognize that has been defeated by Christ.
Dear believer, heed Owen’s advice!
For more advice on killing sin, see the lesson here.