What is Sanctification?
According to the Westminster Shorter Catechism (Q. 35), sanctification is,
“the work of God’s free grace, whereby we are renewed in the whole man after the image of God, and are enabled more and more to die unto sin, and live unto righteousness.”
This moral renovation, in which we are increasingly changed from what we once were, flows from the agency of the indwelling Holy Spirit (Rom. 8:13; 12:1, 2; 1 Cor. 6:11, 19, 20; 2 Cor. 3:18; Eph. 4:22–24; 1 Thess. 5:23; 2 Thess. 2:13; Heb. 13:20, 21). God calls His children to holiness, and graciously gives what He commands (1 Thess. 4:4; 5:23).
Ligonier Ministries says,
Sanctification is an ongoing process, dependent on God’s continuing action in the believer, and consisting of the believer’s continuous struggle against sin. God’s method of sanctification is neither activism (self-reliant activity) nor apathy (God-reliant passivity), but human effort dependent on God (2 Cor. 7:1; Phil. 3:10–14; Heb. 12:14). Knowing that without Christ’s enabling we cannot do good works, but also that He is ready to strengthen us for all we have to do (Phil. 4:13), we “abide” in Christ, asking for His help constantly— and we receive it (Col. 1:11; 1 Tim. 1:12; 2 Tim. 1:7; 2:1).
Romans 8:29 – For those whom he foreknew he also predestined to be conformed to the image of his Son, in order that he might be the firstborn among many brothers.