Throughout Scripture, various motifs are given to describe the Christian life, motifs that can help us understand the way we should act as those who are called by God to be on mission in the world but not to be conformed to it (John 17:14-19). One of these motifs is two kingdoms that exist in tension in this world—the kingdom of Jesus and the kingdom of Satan.
In the New Testament, Jesus and His apostles after Him draw a sharp antithesis between the Kingdom of God and the World, between Christ’s Kingdom and Satan’s, between redeemed and unredeemed humanity. John describes all unredeemed humanity with the term “World,” the dark, sinful, rebellious mass of humanity and spiritual darkness that sets itself up in opposition to God: Jesus came to save this World, yet it is this world that rejected Him and opposes His people (e.g., John 2:15-17, 3:1, 13). Jesus told His disciples that all who were not with Him were against Him (Matt. 12:30, cf. Luke 11:23; Mark 9:40; Luke 9:50). In Ephesians 2:2, Paul describes the Ephesians before God saved them as those “following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of obedience”: they were followers of Satan, “the ruler of this world” (John 12:31: cf. 14:30, 2 Cor. 4:4, Eph. 6:12). All those who are not in Christ are in rebellion against Him (Rom. 1:18-23) and are hostile towards God (Rom. 5:10, 8:6-8). In this way, the NT divides all the earth into two groups, two kingdoms: those in opposition to God, the kingdom of Satan, and those who are in Christ, the kingdom of God. The kingdom of Satan is darkness and rebellion, yet Christians live in it as a light (Matt. 5:14-16; John 8:12; Eph. 5:8; Phil. 2:15). So Christians live in a world hostile towards them and their God, and by their life and words they shine forth in distinction. This implies, at least, that the world in which we live is a battlefield, and we are called to warfare: each and every Christian is called to live in such a way that furthers the Kingdom of God and pushes back the lines of the enemy.
(adapted from the paper, “Appendix 2 – Christ and Culture“)