How does a person resist the devil? Why does resisting the devil cause him to flee?

from the old testament

• Whether as accuser, adversary, or destroyer, it is clear that the devil is the enemy of God and God's people (Job 1–2; Zechariah 3:1–2).
• The devil began with his assiduous assault on Adam and Eve, who were the pinnacle of God's creation on earth. Taking the form of a serpent, he tempted Adam and Eve to distrust God's goodness and steal the one thing that God had forbidden them (Genesis 3; Revelation 12:9). In doing so, the devil succeeded in getting mankind to imitate his own pride and selfish greed. Upon mankind's fall from grace, God promised to send One who would overcome the destruction wrought by the devil. This promised Redeemer would crush the serpent's head and reverse the curse of death and damnation (Genesis 3:15).

from the new testament

• The New Testament confirms that the devil is the enemy of God and His people. (Ephesians 2:2; 1 John 5:19; Revelation 12:9).
• Ever since his ejection from the heavenly sphere, the devil has made it his purpose to destroy the works of God (John 10:10).
• God defeated the devil, as well as sin and death, by sending His only begotten Son, Jesus Christ, to suffer and die for the sins of those who would believe in Him and to rise victoriously over death three days later (1 Corinthians 15:3–4; Hebrews 2:14–15). Where Satan brought a curse, Christ is the cure. Where Satan possessed a serpent to bring death, Christ is likened to the serpent who brings life (John 3:14–15). Christ has conquered the devil (Colossians 2:15). Although an angelic being, the devil is a defeated, finite creature (Revelation 12:9). Although his sentence has been pronounced, the execution of that sentence lies in the future (Revelation 20:10).
• While awaiting his judgment, the devil seeks to inflict as much damage as is possible while he is still free to roam the earth. In fact, Scripture compares him to a lion roaming about, seeking someone to devour. As such, we must always be alert and on guard against his wiles and tactics (1 Peter 5:8).
• God commands us to resist the devil and promises that if we do so, the devil will run away from us. James 4:7 says, "Submit yourselves therefore to God. Resist the devil, and he will flee from you."
• It is of primary importance to point out that we resist the devil by the power of God, not on our own (see Zechariah 4:6; John 15:5; 2 Corinthians 12:9).
• The first step to resisting the devil is submitting to God. We are made right with God through the sacrifice of Jesus Christ, and then we submit to Him by responding to the Holy Spirit's work in our lives. God has given His Spirit, the Spirit of Christ, to all who trust in Christ for salvation (Romans 8:9).
• The same Spirit that enabled Christ to successfully ward off the devil's forty-day campaign in the desert has been given to believers (Mark 1:13).
• Additionally, God has not left us defenseless in our battle against that ancient evil dragon, but has provided us with a complete set of armor (Ephesians 6:10–20). God has given us the belt of truth, the breastplate of righteousness, gospel shoes, the shield of faith, the helmet of salvation, the sword of the Spirit, and prayer.
• The devil must flee when we resist him with spiritual weapons because He who lives in us (Jesus Christ) is greater than the devil (1 John 4:4).
• Just as the demons cower and shriek in frightful terror before the presence of Christ, the devil must flee from us when we resist him because Christ dwells in us (Matthew 8:29; Romans 8:10; Colossians 1:27).
• Christ has triumphed over the devil's attacks and accusations by defeating the powers of sin and death (1 Corinthians 15:54–57).
• When the devil accuses a Christian of sin and guilt, the Christian can appeal to the blood of Christ (Ephesians 2:13; Hebrews 9:26). God has thoroughly equipped the believer in Christ to resist the devil and cause him to flee.

implications for today

Having been created by God as the highest of the angelic beings, Satan did not remain content with his position but sought to exalt himself above God (Isaiah 14:12–15; Ezekiel 28:12–17). His pride and desire for power led to his downfall, resulting in God casting him out of heaven, along with the angels who joined his rebellion, now known as demons (Revelation 12:7–9; 2 Peter 2:4; Jude 1:6). Because of their rebellion, the devil and his demons will spend eternity in the lake of fire prepared for them (Matthew 25:41). Until then, the devil and his demons are seeking to bring down as many with them as possible.

God has given us all we need to resist the devil. The truth of God's Word, the sword of the Spirit, acts as both a defensive and offensive weapon. God's truth protects us from the devil's lies and is used to proclaim the truth of the gospel. Our loins are to be girded with truth, meaning that the truth of God provides stability and core support. A "belt" is also a place where flowing tunics could be gathered up to enable feet to move freely. God's truth gives us not only structure and support, but freedom to not be entangled (John 8:31–33; Hebrews 12:1–2). The righteousness that comes through faith in Christ acts as a breastplate and shield to protect us from the devil's assaults to our hearts (Romans 3:22; Philippians 1:11). The gospel shoes give us peace, which enables us to stand firm and also to move in the direction God calls. The shield of faith enables us to "extinguish all the flaming darts of the evil one" (Ephesians 6:16). When Satan accuses us or tempts us to doubt God, faith acts as our protector. The helmet of salvation secures our minds. First Corinthians 2:16 says that "we have the mind of Christ." Romans 12:2 tells us to "be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect." The helmet of salvation assures us that we are eternally saved by God. And it also functions as a sort of ongoing salvation in delivering us from the power of sin. When our minds are secure in Christ, we can better resist the devil. An often-forgotten weapon in the battle against the devil is prayer. In some of the most crucial moments in the life of Christ, He prepared Himself through prayer (Matthew 26:36–46; Hebrews 5:7).

All of these spiritual weapons are wielded by believers in the power of the Spirit through faith in Jesus Christ. God has provided everything we need to defend ourselves against the cunning and devious attacks of he who disguises himself as an angel of light (2 Peter 1:3; 2 Corinthians 11:14). By faith in Christ and in the power of the Spirit, we overcome both the world and the devil (1 John 5:4–5). We resist the devil when, like Christ, we resist temptation. We resist the devil by refusing to worship anyone or anything other than God (Matthew 4:8–10). We resist the devil by refusing to put God to the test by being careless and reckless in our spiritual lives (Matthew 4:5–7). We resist the devil by living on the very Word of God and not merely on bread (Matthew 4:2–4).