To be sanctified (Heb. קָדָשׁ qadash Grk. ἁγιάζω hagiazo) means to be set apart. God’s essential nature is holy; therefore, He is set apart as righteous (Lev. 11:44-45). In God’s creation, sanctification has the idea of being set apart for special purpose. In the OT, sanctification included certain days (Gen. 2:3; cf. Ex. 20:8), people and animals (Ex. 13:2), the nation of Israel (Ex. 19:6), and everything associated with worship, including the altar, its utensils, the laver for washing, and those who executed the priestly ceremonies (Ex. 40:10-13). In the NT, we are said to be positionally sanctified in union with Christ (1 Cor. 1:2; Heb. 10:10, 14), experientially sanctified because of our obedience to God’s Word (John 17:17; 1 Pet. 1:14-16), and will be eternally sanctified when we leave this world and enter heaven (1 John 3:1-3; Rom. 8:29-30; Jude 24-25).
Positional and eternal sanctification are accomplished entirely by God (monergism). However, experiential sanctification is a collaboration (synergism) in which God directs and empowers us to be set apart from the world to do His will (John 17:17; 1 Pet. 1:14-16). The means of experiential sanctification is by learning and living God’s Word (John 17:17; Rom. 12:1-2; Eph. 4:1, 11-14; Col. 3:1-2; 2 Tim. 2:15; 3:16-17; 1 Pet. 2:2; 2 Pet. 3:18), and walking in dependence on the Holy Spirit (Eph. 5:18, Gal. 5:16, 25). The place where sanctification occurs is in Satan’s world (John 17:14-16; cf. 15:19).
Believers live in a world that is currently under Satan’s control. Like Joseph in Egypt, or Daniel in Babylon, we serve as God’s ambassadors to a fallen world that is hostile toward us. Some Christians seek to avoid worldly conflict by withdrawing from it, pursuing monasticism; whereas others avoid conflict by embracing the world and its values. Biblically, we are to be in the world, in regular contact with unbelievers, graciously lovingly and living God’s will in opposition to the world’s values, and sharing Christ with those who will listen. We cannot change the world, but we can avoid being forced into its mold by learning and living God’s Word, and sharing the Gospel message that others might be saved out of it. God Himself will eventually destroy Satan and his world-system and will create a new universe. Until then, “according to His promise we are looking for new heavens and a new earth, in which righteousness dwells” (2 Pet. 3:13).