The Bible speaks of our being sanctified by the Word of God as well as by the blood of Christ and by the Holy Spirit.
Just as Christ is not of the world, so the believer is not of the world. God uses His Word, under the power and work of the Holy Spirit, to bring about the changes He wants in our conduct.
Concerning this our Saviour prayed in John 17:16-19, "They are not of the world, even as I am not of the world. Sanctify them through thy truth: thy word is truth. As thou hast sent me into the world, even so have I also sent them into the world. And for their sakes I sanctify myself, that they also might be sanctified through the truth."
This sanctification by the Word of God is a continuous process; it goes on from day to day. Obviously, in order to be set apart by the Word of God, we must learn to know the Word of God.
Some people are not separated from the old life of sin as they should be, even though they have made a profession of faith in Christ. The reason is not necessarily that they are not born again but that the Word of God does not have the place in their lives it should.
The Holy Spirit indwells them, but because they have not studied the Word of God and allowed the Spirit to apply it to their lives, they have not experienced the purification and cleansing that follows.
"Now ye are clean through the word which I have spoken unto you" (John 15:3).