What is sanctification?
Sanctification is a work of God’ s grace, whereby they whom God hath, before the foundation of the world, chosen to be holy, are in time, through the powerful operation of his Spirit (Eph. 1:4, 1 Cor. 6:11, 2 Thess. 2:13) applying the death and resurrection of Christ unto them, (Rom. 6:4–6) renewed in their whole man after the image of God; (Eph. 4:23–24) having the seeds of repentance unto life, and all other saving graces, put into their hearts, (Acts 11:18, 1 John 3:9) and those graces so stirred up, increased, and strengthened, (Jude 20, Heb. 6:11–12, Eph. 3:16–19, Col. 1:10–11) as that they more and more die unto sin, and rise unto newness of life. (Rom. 6:4,6,14, Gal. 5:24)
The Westminster Larger Catechism: With Scripture Proofs. (Oak Harbor, WA: Logos Research Systems, Inc., 1996).