Sanctification—our growth in holiness—is a process that lasts from the moment of our conversion until we are glorified in heaven. God definitively sets us apart as His holy people when we turn to Christ, and so we can be called “saints” (Eph. 1:1). However, becoming holy in practice takes time and a single-minded commitment to do what the Lord calls us to do as citizens of His kingdom (Luke 16:16). We are saints, and yet we must become saints—we must have a righteousness that exceeds that of the Pharisees, a holiness that consists both of external acts of obedience and an internal disposition of love for God and neighbor (Matt. 5:20; 22:34–40).
Ultimately, our growth in holiness is fueled and sustained by God Himself, who works in us to will and to work for His good pleasure (Phil. 2:12–13). But this does not mean we are passive. Instead, we must fight against those foes who would try to take our eyes off of Christ. Traditionally, Christian theologians have identified our three chief foes as the world, the flesh, and the devil.
To call the world our enemy is not to say that we are at war with creation itself. God made the physical world “very good” in its original state, and we steward it for our benefit and His glory (Gen. 1). The world against which we must wage war, rather, consists of the fallen system that resulted when Adam fell and was cast out of Eden (chap. 3). Since the fall, creation has been infected with pride, lust, and all manner of ungodliness. The people who belong to this system because they have not been regenerated hate Christ and all who are united to Him by faith alone (John 7:7). And though sometimes opposition from the fallen world is overt and even consists of persecution, perhaps more often it opposes us by seeking to infect us with its values.
The fallen world’s systems, then, have no love for the things of God. However, God loves this fallen world, and He has sent Christ into the world to save it and has appointed us as His emissaries to take the message of salvation to everyone (John 3:16; 20:21; see Matt. 28:18–20). As ambassadors of the kingdom, we must not conform to this fallen world but must bring the gospel to it. We must be in the world and yet not of the world (John 17:14–16). That is, we do not withdraw into a closed community of Christians but form our affections by the Word of God in the church and then go into the world with the gospel, able to resist the world in the power of the Holy Spirit.