I have been reading through the classic work Of Mortification of Sin in Believers by the puritan John Owen. In addition to having a really catchy title, this book is chocked full of pastoral wisdom about the daily, constant duty of Christians to mortify (i.e., kill) the indwelling sin that resides in us.
Certainly we affirm the truth of the gospel which tells us that Jesus paid the full price for all of our sins past, present, and future. We are completely justified by faith in Jesus, which gives us peace with God (Romans 5:1). Our justification grants us complete forgiveness of our sins, and a righteous standing before God.
However, our justification does not completely eliminate our current sin problem. News flash: Christians still sin.
We know this. Even though our souls are redeemed, our flesh is still corrupt. And the New Testament warns us about the war that ensues between the Holy Spirit, who now is within us, and the flesh. They are mortal enemies. They will battle one another as long as we are on earth (Galatians 5:17).
This is where Owen gives golden counsel about how important it is that Christians realize this active battle that is taking place within us. It is very easy for Christians to live on cruise control and not recognize that within our very beings there is an epic war raging. Because this battle is real, we can never afford to ignore it. We must be continually and aggressively attacking and seeking to kill our sin by the power of the Spirit.
If, then, sin will be always acting, if we be not always mortifying, we are lost creatures. He that stands still and suffers his enemies to double blows on him without resistance will undoubtedly be conquered in the issue.
If we don’t actively acknowledge the battle that is raging against our flesh, and if we are not taking proactive measures to fight against the sin inside of us, then, as Owen warns, we will be conquered and overwhelmed by our sins.
If sin be subtle, watchful, strong, and always at work in the business of killing our souls, and we be slothful, negligent, foolish, in proceeding to the ruin thereof, can we expect a comfortable event?
John Owen, Of Mortification of Sin in Believers –Taken from Overcoming Sin & Temptation Three Classic Works