In his book, Redemption Accomplished and Applied, John Murray writes the following about the sanctification of the believer in Christ:
There is a total difference between surviving sin and reigning sin, the regenerate in conflict with sin and the unregenerate complacent to sin. It is one thing for sin to live in us: it is another for us to live in sin. (p.145)
If you are a Christian and you struggle with sin . . . welcome to the club! That is not a cause for worry or despair. The work of the Lord in your sanctification is ongoing; it is lifelong. You will spend the rest of your life repenting of sin, and you will do that because of the grace of God at work in you!
The time to worry (as Murray says) is if you are complacent in and about your sin. That is a sign that sin is still reigning in your life. It is a sign that, despite whatever profession of faith you may have made, you are simply not yet a Christian.
But if you are a believer in Christ, you are no longer a slave to sin. As Paul writes in Romans 6:20-23,
For when you were slaves of sin, you were free in regard to righteousness. But what fruit were you getting at that time from the things of which you are now ashamed? For the end of those things is death. But now that you have been set free from sin and have become slaves of God, the fruit you get leads to sanctification and its end, eternal life. For the wages of sin is death, but the free gift of God is eternal life in Christ Jesus our Lord.
It is vitally important that we understand the difference between “surviving sin and reigning sin.” The better we understand not only the nature of our justification, but our sanctification in Christ as well, the better equipped we will be to deal with our sins and the doubts that sometimes accompany them.
Justification is an “act of God’s free grace, wherein He pardons all our sins, and accepts us as righteous in His sight, only for the righteousness of Christ imputed to us, and received by faith alone” (Westminster Shorter Catechism Q.33). So we are not justified by anything that we do (not by any righteousness of our own!), but only on the basis of the perfect righteousness of Christ, accounted to us by faith alone!
And sanctification is “the work of God’s free grace, whereby we are renewed in the whole man after the image of God, and are enabled more and more to die unto sin, and live unto righteousness” (Westminster Shorter Catechism Q.35). So, unlike justification (which is a one-time act of God’s grace), sanctification is the ongoing work of God’s free grace in the life of a believer, conforming us more and more into the image of Christ.
Understanding the work of God’s grace in our sanctification (like the act of His grace in our justification) is a key to experiencing the assurance of our salvation in Jesus Christ. In fact, truly understanding the difference between the two (our justification and our sanctification) is one of the keys to experiencing the assurance of our salvation.
And God most certainly does want every one of us who believes in the name of Jesus Christ to know that we have eternal life (1 John 5:13).
Who said that theology wasn’t practical!