It is a major theme throughout the Word of God that Jesus has already defeated the devil. It says He who sins is of the devil, for the devil has sinned from the beginning. For this purpose, the Son of God was manifested, that He might destroy the works of the devil.1 John 3:8 Jesus came to destroy the works of the devil from the beginning of His ministry on earth.
Ultimately, He destroyed and won the final victory over the devil on Calvary. Listen to this “ And having disarmed the powers and authorities, he made a public spectacle of them, triumphing over them by the cross.” Colossians 2:15 He was able to disarm principalities and powers because He became sin and died to defeat death.
The evil one had the power of sin and death over mankind when man fell in the garden. Along came Jesus to destroy the works of the devil. He continually did this as he ministered to Israel. He then died on Calvary and stripped the devil of all the power he had on earth and over man.
Christians need to realize that they have already won the victory over the devil in Jesus. Once a person accepts Jesus as their Lord and Savior they defeat the devil in Christ. His victory becomes ours as we accept the final work of Jesus Christ on Calvary.

The only way that the devil can push us around and destroy our lives is if we let him. Peter says “Be sober, be vigilant, because your adversary the devil walketh about as a roaring lion, seeking whom he may devour.”1 Peter 5:8 He cannot touch us if we don’t let him because he is a defeated foe.
He never wants Christians to know he has been defeated because once they find out they will use their God-given authority against him. Ephesians 6:10-17 is a classic battle passage “Finally, be strong in the Lord and in his mighty power. Put on the full armor of God, so that you can take your stand against the devil’s schemes. For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms. Therefore put on the full armor of God, so that when the day of evil comes, you may be able to stand your ground, and after you have done everything, to stand. Stand firm then, with the belt of truth buckled around your waist, with the breastplate of righteousness in place, and with your feet fitted with the readiness that comes from the gospel of peace. In addition to all this, take up the shield of faith, with which you can extinguish all the flaming arrows of the evil one. Take the helmet of salvation and the sword of the Spirit, which is the word of God. Jesus had defeated the devil once and for all and we have too in Christ.