Sanctification as viewed by historical Calvinists can be summarized quite simply: Putting off the Old and putting on the New Man. As voiced by the preeminent American Calvinist Charles Hodge:
Such being the foundation of the Scriptural representations concerning sanctification, its nature is thereby determined. As all men since the fall are in a state of sin, not only sinners because guilty of specific acts of transgression, but also as depraved, their nature perverted and corrupted, regeneration is the infusion of a new principle of life in this corrupt nature. It is leaven introduced to diffuse its influence gradually through the whole mass. Sanctification, therefore, consists in two things: first, the removing more and more the principles of evil still infecting our nature, and destroying their power; and secondly, the growth of the principle of spiritual life until it controls the thoughts, feelings, and acts, and brings the soul into conformity to the image of Christ. (Hodge, Systematic theology.)
This definition of sanctification emphasizes the progressive nature of the process inherent in the Calvinist doctrine. [ It should be noted that sanctification as discussed here is less a Calvinist only perspective and can be more correctly term Reformed, as many Arminian theologians would agree with the tenets presented.] Calvin himself agrees with the sequence of Christian event placing it after justification and prior to the perfection of glorification.
The reformed picture of the process is that of a progressive increase in the believer’s holiness replacing the inherited corruption that marks all of humanity. This progress continues from the moment of regeneration until the believer returns home to the Lord, rarely without struggles and temporary setbacks. An important distinctive between Calvinists and Arminians (though by no means should it be considered universal to their doctrines) is the idea of perfectionism. The idea that a believer can become perfect, that is completely without sin, in this life is not held within general Calvinist doctrine. Two points in scripture support this postion:
If we claim to be without sin, we deceive ourselves and the truth is not in us. If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness. If we claim we have not sinned, we make him out to be a liar and his word has no place in our lives. (1 Jn 1:8-10).
And Paul’s well known discussion of our struggles:
What shall we say, then? Is the law sin? Certainly not! Indeed I would not have known what sin was except through the law. For I would not have known what coveting really was if the law had not said, “Do not covet.” But sin, seizing the opportunity afforded by the commandment, produced in me every kind of covetous desire. For apart from law, sin is dead. Once I was alive apart from law; but when the commandment came, sin sprang to life and I died. I found that the very commandment that was intended to bring life actually brought death. For sin, seizing the opportunity afforded by the commandment, deceived me, and through the commandment put me to death. So then, the law is holy, and the commandment is holy, righteous and good.
Did that which is good, then, become death to me? By no means! But in order that sin might be recognized as sin, it produced death in me through what was good, so that through the commandment sin might become utterly sinful.
We know that the law is spiritual; but I am unspiritual, sold as a slave to sin. I do not understand what I do. For what I want to do I do not do, but what I hate I do. And if I do what I do not want to do, I agree that the law is good. As it is, it is no longer I myself who do it, but it is sin living in me. I know that nothing good lives in me, that is, in my sinful nature. For I have the desire to do what is good, but I cannot carry it out. For what I do is not the good I want to do; no, the evil I do not want to do—this I keep on doing. Now if I do what I do not want to do, it is no longer I who do it, but it is sin living in me that does it.
So I find this law at work: When I want to do good, evil is right there with me. For in my inner being I delight in God’s law; but I see another law at work in the members of my body, waging war against the law of my mind and making me a prisoner of the law of sin at work within my members. What a wretched man I am! Who will rescue me from this body of death? Thanks be to God—through Jesus Christ our Lord!
So then, I myself in my mind am a slave to God’s law, but in the sinful nature a slave to the law of sin. (Rom 7:7-8:1)
The view of sanctification as a lifelong process through which the Christian will be gradually transformed in holiness, steadily moving in image towards the likeness of our Savior Jesus Christ. It is generally accepted that perfection in holiness will not be achieved until the moment of glorification in the Lord’s presence. This is representative of the majority view of the Protestant Church (Calvinist and Arminian together) and finds it way into the belief systems of most identifying as Christians.