The doctrine of sanctification is not unique to Methodism or Wesleyan Christianity. Holiness is about as biblical as you can get. John Wesley, however, put a distinctive emphasis on sanctification.
The Articles of Religion as borrowed by Wesley from the Anglican Church do not include an article on sanctification. But we get some indication of Wesley’s intentions by his choice to leave out this article from the Church of England’s 39 Articles:
XV. Of Christ alone without Sin.
Christ in the truth of our nature was made like unto us in all things, sin only except, from which he was clearly void, both in his flesh, and in his spirit. He came to be the Lamb without spot, who, by sacrifice of himself once made, should take away the sins of the world; and sin (as Saint John saith) was not in him. But all we the rest, although baptized and born again in Christ, yet offend in many things; and if we say we have no sin, we deceive ourselves, and the truth is not in us.
My hunch is the last sentence is the killer. Although Wesley often quoted 1 John’s teaching that if we say we do not sin the truth is not in us, he – as far as I can tell – always understood that as an affirmation of original sin, which strikes me as a better reading of 1 John than the idea that we are doomed to be active sinners despite the work of grace in us.
Our Book of Discipline does have an article on Sanctification, but it was not one of the original 25. It reads:
Sanctification is that renewal of our fallen nature by the Holy Ghost, received through faith in Jesus Christ, whose blood of atonement cleanseth from all sin; whereby we are not only delivered from the guilt of sin, but are washed from its pollution, saved from its power, and are enabled, through grace, to love God with all our hearts and to walk in his holy commandments blameless.
The relevant article from the Confession of Faith is similar to the article above, although not identical.
We believe sanctification is the work of God’s grace through the Word and the Spirit, by which those who have been born again are cleansed from sin in their thoughts, words and acts, and are enabled to live in accordance with God’s will, and to strive for holiness without which no one will see the Lord.
Entire sanctification is a state of perfect love, righteousness and true holiness which every regenerate believer may obtain by being delivered from the power of sin, by loving God with all the heart, soul, mind, and strength, and by loving one’s neighbor as one’s self. Through faith in Jesus Christ this gracious gift may be received in this life both gradually and instantaneously, and should be sought earnestly by every child of God.
My impression is this is probably the least preached and taught of the classic Wesleyan doctrines. I get the sense that we do not really buy into it. I wonder why that is.