The Reformed tradition has historically argued that God is glorified in transforming sinful men and women "after the image of God," and also that sinners "are enabled more and more to die unto sin, and live unto righteousness." (Westminster Shorter Catechism Question 35)
The sanctification of sinners is indeed a wonder of wonders. But the wonder of what God really does in sanctifying a sinner is completely obscured if we forget that the fundamental thing in all this is that sinful men and women are absolutely unable to transform themselves from children of Adam into glorified vessels fit to bring honor to God. For if left to our own strength, we have neither the willingness nor the power to accomplish this vital work. We cannot grow in grace and bear fruit of the Spirit. Bad trees cannot "make a decision" to bear good fruit. We are unable to break the strangle hold of sin and to end the dominion that it has over every part of our lives. As slaves, we simply cannot decide to be free and then merely pronounce ourselves emancipated. The tyranny and power of our oppressor is too great. Moreover, we will never live up to the absolute perfection that God requires of us. We are by nature neither able nor willing to cooperate with God.
The fact that God is glorified in sanctification just isn't seen to be the wonder that it is until one considers who is sanctified, and who initiates the process. Thus, a central motif underlying the Reformed conception of sanctification is the idea that it too, like our justification and adoption, is a work of God's free grace. In much recent evangelical discussion it has become too easy to think of justification in terms of faith and grace, and sanctification in opposite terms of works and our own natural ability. And of course, when we think of our sanctification in terms of works and natural ability, it is man who receives the glory of sanctification. For the sinner is now seen as his own sanctifier, and not God. In this view God merely provides incentives (rewards) and the power (through the Holy Spirit). All we must do is appropriate what God has made available to all, and thereby somehow achieve sanctification under our own steam, with God helping us if only we ask him.
The Westminster Confession of Faith sets forth the Reformed doctrine of sanctification with unsurpassed clarity. Chapter 13 of the Confession, "Of Sanctification," is carefully placed by the framers of the Confession directly after the treatment of justification (Chapter 11), and adoption (Chapter 12). This is an easy point to overlook, yet one cannot fully understand the Confession's teaching on sanctification without noting that the Confession carefully treats the doctrine of sanctification in relationship to other aspects of the ordo salutis, or "order of salvation." Sanctification does not occur in isolation. As the Confession makes clear, sanctification rightly follows justification and adoption. So while sanctification is distinct from justification, it is nevertheless a necessary adjunct. This means that no one who is justified remains unsanctified, and no one will be sanctified apart from prior justification. Just as we are justified by grace through faith because of Christ, so too, we are sanctified by grace, through faith, because of the work of the Holy Spirit.
It is easy to err, as many of our contemporaries do, by confusing sanctification with justification ("I will die justified if I am able to attain a certain level of holiness") or by separating the two as if they had no relationship whatsoever (that is, "I can accept Jesus as my 'Savior' without confessing him Lord as over every area of my life"). As the Confession points out, sanctification (which is a work of God in us), is closely related to effectual calling (Chapter 16) and good works (Chapter 16), and follows as an effect, the cause being justification. Every sinner who has placed his trust in Christ, and has the guilt of his sin imputed to Jesus Christ, who makes full satisfaction for it, and in turn has the perfect righteousness of Christ reckoned to him as if it were his own, is justified. This same person inevitably grows in sanctification.
The Confession is clear about the relationship between sanctification and other doctrines. G. I. Williamson summarizes the main points that the Confession makes about sanctification: Chapter 13 teaches us that the regenerate nature in believers is, by God's Word and Spirit, enabled to develop, that in this development the believer dies more and more unto sin and lives more and more unto righteousness, that this work of sanctification pervades the whole man, that complete victory over sin is not attained in this life, but that genuine progress is made in that all true believers do strive to perfect holiness in the fear of God.
Many evangelicals reading the Confession for the first time may be somewhat surprised to notice how different it sounds from teaching on sanctification in many Bible churches. The focus in the Confession is on God acting upon us and God acting in us through specific means. There is no list of things that we must do to sanctify ourselves, and there is no corresponding list prohibiting those things that American evangelicals historically have found to be evil. This is strong evidence of just how far evangelicals have departed from historic Protestant, biblical teaching, and why evangelicals so desperately need the historic Protestant confessions. Too many Christian leaders try to reinvent the theological wheel; they don't do as well as their theological forebears. Instead, the focus of the Confession is strictly theological.
First and foremost, the Confession makes it clear that sanctification is a continuation of our regeneration. God not only begins the Christian life with regeneration, he brings it to fruition. "They who are effectually called and regenerated, having a new heart and a new spirit created within them, are farther sanctified really and personally, through virtue of Christ's death and resurrection, by his word and Spirit dwelling in them (13.1)." Once God begins the process in the new birth, he brings it to completion through sanctification. As A. A. Hodge points out, "the grace implanted in them [is] developed more and more." Notice, too, that sanctification is directly connected to the word of God and to the indwelling Holy Spirit. The Confession is careful to associate the operation of the Holy Spirit in bringing the power of Christ to us by the reading of the Word. Therefore, man-made rules and techniques for increasing personal holiness are not only useless in bringing true sanctification, but they are hindrances to it since they must obscure the primary means of sanctification that is the word of God.
Next, the Confession defines what sanctification actually entails. "The dominion of the whole body of sin is destroyed, and the several lusts thereof are more and more weakened and mortified, and they more and more quickened and strengthened in all saving graces, to the practice of true holiness, without which no man shall see the Lord." Here perhaps more clearly than anywhere else, the Confession focuses on the meaning of sanctification, rather than on applications and practices to attain it. Some perfectionist schemes argue that only a few of God's people, spiritual élites, can attain the level of holiness expected by God. But the confession makes it clear that the promise of sin's broken dominion is for all Christians. Our sinful nature is steadily weakened and diminished, in what Reformed theologians call progressive sanctification. Since the dominion of sin is completely broken at conversion, every Christian is already sanctified in a sense (1 Cor 6:11), and this is why the Bible expressly calls all Christians saints (Rom 1:7). This is what is known as definitive sanctification.
The confession points out a third aspect of sanctification; that is, it extends to the entire person. There is no part of us that God leaves unsanctified. God not only sanctifies the soul, he sanctifies our minds, emotions and wills as well. There is no radical dichotomy in our sanctification, where God supposedly sanctifies the spiritual part of the Christian, and then leaves the rest of the person completely corrupted by Adam's fall. Since God indeed sanctifies the entire person, new birth and sanctification inevitably manifest themselves in a cooperative effort with the grace of God.
A. A. Hodge makes the point nicely. "It must be remembered that while the subject is passive with respect to that divine act of grace whereby he is regenerated, after he is regenerated he cooperates with the Holy Ghost in the work of sanctification. The Holy Ghost gives the grace, and prompts and directs in its exercise, and the soul exercises it. Thus while sanctification is a grace, it is also a duty; and the soul is both bound and encouraged to use with diligence, in dependence upon the Holy Spirit, all the means for its spiritual renovation, and to form those habits resisting evil and of right action in which sanctification so largely consists." The fruits of sanctification are good works because God has changed us in regeneration, as it were, from a bad tree that can only produce bad fruit, into a good tree, that can begin bearing good fruit. There is a corresponding change from someone completely unwilling and unable to cooperate, into someone who does. By sanctifying the entire person, God continually works in us so that "it is the work of God, and it is the work of man, assisted by supernatural grace."
The Confession discusses a fourth quality of sanctification--it is never perfected in this life. That is, there is no such thing as "Christian perfection" as taught by John Wesley, or "entire sanctification" taught by Charles Finney. Closely following the language of Paul in Romans seven, the Confession explains that while "sanctification is throughout in the whole man, yet imperfect in this life; there abideth still some remnants of corruption in every part, whence ariseth a continual and irreconcilable war, the flesh lusting against the spirit, and the spirit against the flesh." (13.2)
Every Christian is made new and wants to do good, and yet there exist the dethroned, but highly destructive remnants of indwelling sin, which will oppose this new self to the death. Williamson accurately describes this war with indwelling sin. "The dominion of sin is broken, though the presence of sin is not entirely eliminated. ...Sin no longer commands the heart. The main lines of communication have been destroyed. The control center is in the hands of God. But the alien force still carries on harassment of all kind of skill, cunning, and desperation of a defeated foe. ...It is a noteworthy fact that the greater progress one makes in sanctification the more will he be distressed by the sin that yet is present with him." The sinful nature is not completely eradicated. Though defeated and weakened, it remains, and becomes the source of much struggle and misery in Christian life. For while the dominion of sin is broken, there will be constant guerilla warfare until the believer is finally united with Christ. Some may question whether or not they have ever really trusted in Christ, because they continually struggle with specific and problematic sins. The struggle itself is the very sign that God is indeed sanctifying them.
The Confession stresses that all Christians will make genuine progress and growth in holiness. "In which war, although the remaining corruption for a time may much prevail, yet, through the continual supply of strength from the sanctifying Spirit of Christ, the regenerate part doth overcome; and so the saints grow in grace, perfecting holiness in the fear of God." (13.3) Since it is God who regenerates us and sanctifies us, he will ensure ultimate victory over sin. Though we certainly may feel in the midst of the struggle that we will never have victory over sin, God promises that in the end, every Christian will be sanctified. Paul himself makes clear, "being confident of this, that he who began a good work in you will carry it on to completion until the day of Christ Jesus." (Phil 1:6) When we see sanctification from the perspective of the Westminster Confession, we see that it is indeed a wonder of wonders as sinful men and women are transformed from children of wrath into vessels of glory. Since God is the author and finisher of this process, he receives all the glory. God is glorified in the sanctification of sinners!