Sanctification is an English word used to express a concept that occurs throughout the Bible. The Hebrew qadosh occurs in different forms 830 times in the Old Testament. As a noun or an adjective it is most frequently translated "holy" or "holiness," while its verb forms are usually translated "sanctify." In the Greek New Testament the comparable word is hagios which occurs in all of its forms 268 times. It has basically the same range of meanings as qadosh.
A Holy God. The concept of sanctification has its roots in the nature of God who is entirely separate from His people. Thus people or objects which are given over to God's service must be used for Him alone. Furthermore, they must not act or be used in any way that is contradictory to His moral character, which is marked by love, purity, and selflessness. People and objects thus devoted to God are referred to as sanctified (that is, "made holy").
Holiness Commanded. The remarkable thing about Old Testament teaching on sanctification is that God wants all His people to be holy as He is holy (Leviticus 19:2). He is not content for only a few priests to share His character; He expects all who bear His name to display these qualities. God's righteous nature is the very opposite of sin, and He asks His people to be like Him in this respect. He enables them to become such persons when they separate themselves from sin and devote their lives entirely to God (Leviticus 20:7, 8; Isaiah 6:1-8).
Christians widely recognize that this same expectation carries over into New Testament teaching as well (1 Thessalonians 5:23, 24; 1 Peter 1:15, 16). It is by means of the Holy Spirit's filling the life of the believer with Himself that this holy living becomes possible (John 14:15, 16). However, not all are agreed as to the extent to which this holy living becomes possible, nor about the precise mode whereby the Holy Spirit fills the life of the believer.
Some contend that God both forgives sin and imparts the sanctifying Holy Spirit at the moment of conversion. From that point on, all further sanctification is achieved only by personal discipline, habit formation, and gradual growth in Christlikeness. Such persons understand that Jesus' promise of the Holy Spirit (Matthew 3:11; John 7:38, 39; 16:7, 8; Acts 1:5, 8) was intended as a separate and distinct experience only for the disciples in the Upper Room on the Day of Pentecost. Since that time, this special gift of the Father has come to Christians as a part of the conversion experience.
The Wesleyan Understanding. In contrast, many others believe that the gift of the Holy Spirit in sanctifying power was promised as a distinct personal experience for all Christians (Matthew 3:11; John 17:20). Just as the disciples genuinely believed in Christ before Pentecost and yet needed the filling of the Holy Spirit before they could experience all that God had for them, so do all believers. Thus God's plan to equip His people for holy living is not complete until we are sanctified completely by seeking and experiencing . personal filling with the Holy Spirit.
God begins His work of sanctification when we are converted. He who becomes a follower of Christ is given new spiritual life, a life of loyalty and love for God. This is accomplished by the Holy Spirit (Romans 8:9). The Bible describes this work of the Spirit as a "new creation," being "born again," "born of the Spirit," "passing from death to life," being "quickened with Christ." To this extent all Christians are sanctified when they are converted; the Holy Spirit is active in their lives, although not yet in the fullness that Jesus promised.
This transformation that Christ gives when we are saved is called initial sanctification. It is the beginning of purification and holiness. However, completion of that process is not to be achieved merely by Spirit-aided human effort. Rather, just as forgiveness of sins is freely given by God for Christ's sake when we ask, so is a holy heart.
The Sinful Nature Must Be Cleansed. This second work of grace through faith is known as entire sanctification. It is necessitated by the twofold nature of sin. It is not enough to be forgiven for sins committed in the past; it is also necessary that Sin, the extreme hostility to God which prompted the sins, be cleansed. It is apparent that this cleansing is not completed in initial sanctification. In such passages as Colossians 3:5 17 Paul urges his readers to a further radical surrender to God.
Growth Is Necessary. Entire sanctification does not imply absolute perfection, nor that further growth in grace is unnecessary. In fact, Wesley specifically chose the term to distinguish what was accomplished in a moment of crisis from the process of growth in holiness which is lifelong for the believer. Nevertheless, this process will be frustrated unless at the appropriate moment of conviction the believer exercises faith for the fullness of the Holy Spirit.
One concise way of expressing the foregoing is: "Sanctification is initiated at the moment of justification and regeneration. From that moment there is a gradual or progressive sanctification as the believer walks with God and daily grows in grace and in a more perfect obedience to God. This prepares for the crisis of entire sanctification which is wrought instantaneously when the believer presents himself a living sacrifice, holy and acceptable to God, through faith in Jesus Christ, being effected by the baptism with the Holy Spirit who cleanses the heart from all inbred sin. The crisis of entire sanctification perfects the believer in love and empowers him for effective service. It is followed by lifelong growth in grace and knowledge of our Lord and Savior, Jesus Christ. The life of holiness continues through faith in the sanctifying blood of Christ and evidences itself by loving obedience to God's revealed will" (The Discipline, The Wesleyan Church).
Biblical Foundations. These statements of belief reflect what the Bible teaches in many passages, including the following (from the Manual, The Church of the Nazarene):
For All Christians. These scriptures mean that God makes His Spirit and His holy character available to us in this life—in answer to our earnest desire and faith for Him. The baptism with the Holy Spirit is "the gift of the Father" available to every follower of Christ. Jesus prayed that His first disciples might be sanctified (John 17:17). What He asked for them, He asked for all "those who will believe in Me through their word" (John 17:20). What He asked for His early followers He poured out on them at Pentecost, and He waits to give the same Holy Spirit to His disciples who seek for Him today.
Four questions must be asked: (1) If these scriptures do not teach a present holiness, what do they teach? (2) Is there a hunger in the spirit of any Christian to experience more of God's holiness? (3) Where there is such hunger, why not accept as a personal promise Jesus' offer to send another Helper (John 16:6, 7)?
All Christians who hunger and thirst after righteousness should follow Jesus' instructions to "wait for the Promise of the Father"; to seek until "baptized with the Holy Spirit" (Acts 1:4, 5).
Multiplied thousands of Christians bear glad witness that when they put their faith in the promises of the Scriptures and followed Jesus' instructions they received the Holy Spirit in His fullness. They testify that God for Christ’s sake cleanses them from inward sin and sanctifies them completely (1 Thessalonians 5:23).
 The Discipline of The Wesleyan Church, 1988 Edition, - copyright ©1989 by Wesley Press.
 Manual of The Church of the Nazarene, 1989 Edition, - copyright ©1989 by Nazarene Publishing House.
Taken from: The Wesley Bible - Copyright ©1990 by Thomas Nelson, Inc.