Sanctification is the radical change God brings about in the heart of a person who trusts Jesus Christ as Savior. It’s the passing from spiritual death to spiritual life, the beginning of a new creation in Christ, and the writing of God’s Law in our hearts. It means a new relationship to the Law of God and a new attitude toward it. And all this is from God, a gift of His grace just as surely as is the gift of justification. God doesn’t bring us into His kingdom, then leave us on our own to grow. He continues to work in our lives to conform us more and more to the likeness of His Son. As Paul said, “He who began a good work in you will bring it to completion at the day of Jesus Christ” (Philippians 1: 6). This continuing work of God is called “progressive sanctification.” It differs from initial sanctification in two respects. Initial sanctification occurs instantly at the moment of salvation when we’re delivered from the kingdom of darkness and brought into the kingdom of Christ (Colossians 1: 13). Progressive sanctification continues over time until we go to be with the Lord. Initial sanctification is entirely the work of God the Holy Spirit who imparts to us the very life of Christ. Progressive sanctification is also the work of the Holy Spirit, but it involves a response on our part so that we as believers are actively involved in the process. The progressive nature of sanctification is implied throughout the New Testament epistles in all those instances where we are exhorted to grow, to change, to put off the deeds of the old man and put on Godlike character.
Bridges, Jerry (2014-02-01). Holiness Day by Day: Transformational Thoughts for Your Spiritual Journey (p. 214). NavPress. Kindle Edition.