Various Views
There have been several views of sanctification propagated during the history of the church. Here is a brief description of the more prominent views.
Pelagianism
The doctrine of Pelagianism is derived from Pelagius, an astute ascetic who lived during the late fourth century and early fifth centuries. Pelagius's view of sanctification/ salvation arose from his particular view of hamartiology. Based on his belief in the special creation of each soul by God, he did not believe that man was born inherently sinful through Adam, but that each person was created free from sin and guilt just as Adam was created in righteousness. We only become sinners when we commit our first sin, but still will not possess a natural bias toward sin. Because we are morally responsible, any sin committed by the Christian is committed by free choice, apart from any unbridled evil passions of the will.
Although Pelagius confessed that sanctification must come by the grace of God, his definition of grace was that of an external aid given by God to illuminate to us our need for holiness, not an internal working of God's Spirit.21 Sanctification, then, comes by the effort of men and their will, unaided by a divine inner-working of God's Spirit.
Purgatorical View
Catholicism maintains that it is possible to be entirely sanctified in this life. One is sanctified by obedience to God's law coupled with grace/faith. If one passes out of this life with sins still on their account they must pass through the purifying fires of purgatory to complete their sanctification. Purgatory, then, is an intermediate place between earth and heaven where the saved dead go to purify their souls from venial sins before entering the holy presence of God. The duration and severity of the purifying depends on the severity of one's sins.22 Time in purgatory can be lessened by special masses, prayers, and alms of the church.
The purgatorical view does not have much to commend it seeing that there is no real Biblical warrant for such a belief in purgatory. The belief is drawn from weak Scriptural statements, the Apocrypha, and the writings of Origen (II Maccabees 12:46; Matthew 5:26; 12:32; I Corinthians 3:11-15). The Scriptures indicate that at death one's spirit goes to heaven or to hell, depending on their relationship with God at the point of death, not an intermediate place of torment to cleanse them from all sin (Luke 23:43; II Corinthians 5:8; Philippians 1:20-23).
Lutheran
Luther understood sanctification to be getting used to our justification. One of the hallmarks of the Lutheran theology of sanctification is his teaching that man is both sinner and saint simultaneously. There is always a dual tension in the life of the believer between these two identities. The law of God and the grace of God are dichotomies, opposed to one another. The law of God reveals God's holiness and our sinfulness, while the grace of God saves us.
Reformed
Sanctification is viewed as both a past reality and present progress. In Reformed theology the basis of our sanctification is our union with Christ (I Corinthians 1:30). We draw our sanctification from Christ's perfect sanctification, and our union with His person. When we are joined to Christ the dominion of sin is broken (Romans 6:6), and our status to sin is changed. Reformed theology does not see a dichotomy between law and grace as did Luther, but sees the law of God as the guide for the justified.
Wesleyan/Keswickian
Although conceptually distinct, the Wesleyan and Keswickian models of sanctification are so compatible that both shall be dealt with together.
Wesleyan sanctification teaches that there is a second work of grace that comes to the believer through a crisis experience, perfecting sanctification (entire sanctification). This grace will perfect the believer in love. John Wesley did not believe that a perfected believer could no longer sin, but rather that they would not sin. Although Wesley recognized that there were sins of ignorance and omission, on a practical level he defined sin purely in terms of volition. Sin is any voluntary act against a known law of God (I John 3:4). Perfection is not sinlessness, but an all encompassing change of life. It is a relative perfection which frees the Christian from willful transgressions against God's law, impure intentions, and pride by eradicating our sinful desires.
Wesley did not see sanctification as a once-for-all status, but in terms of an acquired attribute subsequent to conversion (thus a second work of grace). As did the Catholic church, Wesley blended the concepts of justification and sanctification into one, and thus taught that in order to keep one's justification they must continue in sanctification.
The Keswickian model is hybrid between Reformed and Wesleyan theology. It borrows its view of man's inherent sinfulness and the necessity of holiness growing out of our union with Christ from the former, and the idea of perfection from the latter. Keswick distinguishes between the normal, or carnal Christian and the victorious, or spiritual Christian. The former fail to live by the power of the Spirit, but are being controlled by the lusts of the flesh.23 The latter is the Christian who has a post-conversion crisis experience which catapults them into a life of victory over the sins of the flesh. Believers are responsible to appropriate Christ's victory to their lives, but many Christians live below the dignity of the Christ-filled life.
Keswickian theology, although it also defines a believer's sinlessness in terms of voluntary disobedience to a known law of God, also recognizes that there are sins of the heart and sins of omission. We will never attain sinless perfection until our death/ glorification because we are inherent sinners. The sin nature will never be eradicated in this life, but it is overwhelmed by the influence of the indwelling Spirit of God.24 There are, then, two levels of sin in Keswickian theology: theoretical, practical. When we do commit sin we are thrown out of fellowship with God. Since we can never please God in and of ourselves we must allow Christ to take over in our lives.
Evangelical
Evangelicals see a relationship between justification and sanctification, but distinguish them conceptually so that one's justification before God is not seen to be dependent on one's level of sanctification. Sanctification is positional and progressive. Borrowing from Luther, evangelicals maintain that man is both righteous and a sinner simultaneously. Man works with God to grow in holiness, by the grace of God. The Westminster Shorter Catechism (1647) provides the following answer to the nature of sanctification which succinctly defines the evangelical view: "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."25