You were formerly darkness, but now you are light in the Lord; walk as children of light
Ephesians 2:1-3 describes our nature before we came to Christ: "You were dead in your trespasses and sins, in which you formerly walked according to the course of this world, according to the prince of the power of the air . . . and were by nature children of wrath." Before we became Christians our very nature was sin, and the result of our sin was death (separation from God). As such we served ourselves and Satan as a matter of course.
But at salvation God changed our very essence; we became ". . . partakers of the divine nature, having escaped the corruption that is in the world by lust" (2 Peter 1:4). You are no longer in the flesh; you are in Christ. You had a sinful nature before your conversion, but now you are a partaker of Christ's divine nature. You are neither eternal nor divine, but you are eternally united with Christ's divinity. Paul said it this way: "You were formerly darkness, but now you are light in the Lord; walk as children of light" (Ephesians 5:8); "Therefore if any man is in Christ, he is a new creature" (2 Corinthians 5:17). In the face of Satan's accusations that we are no different, we must believe and live in harmony with the fact that we are eternally different in Christ.
The New Testament refers to the person you were before you received Christ as your old self ( old man in the King James Version ). At salvation your old self, which was motivated to live independently of God and was therefore characterized by sin, died (Romans 6:6), and your new self, motivated by your new identity in Christ and characterized by dependence on God, came to life (Galatians 2:20).
Your old self had to die in order to sever your relationship with sin which dominated it. Being a new person doesn't mean that you are sinless (1 John 1:8). But since your old self has been crucified and buried with Christ, you no longer need to sin (1 John 2:1). You sin when you choose to act independently of God.
Prayer: Lord, thank You for the hope that comes from knowing that my old self is dead and that I am now a new creature in Christ.