John Owen’s classic The Mortification of Sin includes these words in the preface, where Owen explains why he chose to publish the work:
This was seconded by an observation of some men’s dangerous mistakes, who of late days have taken upon them to give directions for the mortification of sin, who, being unacquainted with the mystery of the gospel and the efficacy of the death of Christ, have anew imposed the yoke of self-wrought-out mortification on the necks of their disciples, which neither they nor their forefathers were ever able to bear. A mortification they cry up and press, suitable to that of the gospel neither in respect of nature, subject, causes, means, nor effects; which constantly produces the deplorable issues of superstition, self-righteousness, and anxiety of conscience in them who take up the burden which is so bound for them.
In other words, trying to kill sin with the weapon of mere self-effort will get you nowhere. We cannot kill sin with the law, for sin only hijacks the law and uses it as the occasion to produce more sin (Romans 7:7-25).
This is why we must go to the gospel. In fact, one paragraph later Owen refers to a true, biblical attack against sin as “gospel mortification.” What this means is that our fight against sin is empowered by the gospel, the good news of Christ crucified and risen for us. The fight against sin is not a fight to make ourselves better. It is a fight to strengthen our faith in the promise of God. For all true obedience to God is born of faith (Hebrews 11), and anything that is not from faith is sin (Romans 14:23).
When you fight against sin, where should your focus be? It should be on God’s promise of a greater joy to be found in Christ than in sin. Lift your mind to Christ crucified, risen, and now interceding for you at the right hand of God, and know that if he presents his blood before the Father on your behalf, he will save you to the uttermost, not only from the penalty of sin, but also from its power. Rest in him, and find the power of sin broken.
This is not an easy thing to do. It is not a matter of passive resignation. It is a fight, because the world, the flesh, and the devil are eager to attack our faith and seduce us with false promises. But constantly coming back to the gospel through Word and sacrament, in the fellowship of the local church, is what stirs our faith and keeps us in the fight.
Don’t fight sin by trying harder to do better. Fight it by believing more earnestly that God is for you in Christ. This is gospel mortification.