“For I know that nothing good dwells in me, that is, in my flesh; for the willing is present in me, but the doing of the good is not. For the good that I want, I do not do, but I practice the very evil that I do not want. But if I am doing the very thing I do not want, I am no longer the one doing it, but sin which dwells in me.
I find then the principle that evil is present in me, the one who wants to do good. For I joyfully concur with the law of God in the inner man, but I see a different law in the members of my body, waging war against the law of my mind and making me a prisoner of the law of sin which is in my members. Wretched man that I am! Who will set me free from the body of this death? Thanks be to God through Jesus Christ our Lord! So then, on the one hand I myself with my mind am serving the law of God, but on the other, with my flesh the law of sin.” Romans 7:18-25
Although Jesus has conquered Satan and his hosts, they still push the battle. They are defeated but not yet confined to their final destiny - the lake of fire.
In his book, The Cross of Christ, author John R. W. Stott explains the tension in this manner: “For though the devil has been defeated, he has not yet conceded defeat. Although he has been overthrown, he has not yet be eliminated. In fact, he continues to wield great power....On the one hand we are alive, seated and reigning with Christ...with even the principalities and powers of evil placed by God under His (and therefore our) feet; on the other hand we are warned that these same spiritual forces have set themselves in opposition to us so that we have no hope of standing against them unless we are strong in the Lord’s strength and clad in his armour....The tension is part of the Christian dilemma between the ‘already’ and the ‘not yet.’ Already the kingdom of God has been inaugurated and is advancing; not yet has it been consummated.”
The victory over the devil was won at the cross. The battle still rages but the Victor lives in you. Place your faith in the finished work of Christ on the cross and you will always be led in His triumph.