How must saints respond to sin in their lives? The Apostle Paul answers, “Put to death [or mortify] therefore what is earthly in you” (Col. 3:5-7 ESV).

Puritan John Owen’s comments, first published in 1656:

“Do you mortify? So you make it your daily work? You must always be at it while you live; do not take a day off from this work; always be killing sin or it will be killing you…Indwelling sin always abides while we are in this world; therefore, there is always a need for it to be mortified. Some have wrongly and foolishly believed that we are able in this life to keep the commands of God perfectly and are wholly and perfectly dead to sin. Through ignorance of the true life in Christ and His power in believers, they have invented a new righteousness that is not in the gospel. They are vainly puffed up by the fleshly minds. Indwelling sin continues to live in believers in some measure and degree while we are in this world. We should not speak as though we had already attained, or were already perfect (Phil. 3:12). Our ‘inner nature is being renewed day by day’ while we live (2 Cor. 4:16); and according to the renovations of the new are the breaches and decays of the old. While we are here we ‘know in part’ (1 Cor. 13:12). There is a remaining darkness to be gradually removed by our growth in the knowledge of our Lord Jesus Christ (2 Pet. 3:18); and ‘the flesh lusteth against the Spirit, so that we cannot do the things that we would’ (Gal. 5:17 KJV). We are therefore defective in our obedience as well as in our light (1 Jn. 1:8). We have a ‘body of death’ (Rom. 7:24); from which we are not delivered by the death of our bodies (Phil. 3:21). It is our duty to mortify, to be killing the sin while it is in us. We must be at this work. He that is appointed to kill an enemy, has only done half his work if he quits before the enemy is dead (Gal. 6:9; Heb. 12:1; 2 Cor. 7:1).”