Inner Spirit and Outer Flesh
The problem of sin for believers stems from the struggle between the new inner spirit and our old sinful flesh (our old sinful self). Since our spirits are no longer slaves of sin, we must no longer obey the lusts and desires of our flesh (Rom 6:12; 8:12). Although sinful desires reside in the flesh, we must consider ourselves dead to sin (Rom 6:11; Col 3:5).
The only way we can overcome sin in this way is by walking in the Spirit. Paul says that if we live by the Spirit, we will “put to death the deeds of the body” (Rom 8:13). Where we choose to set our mind makes the difference between life and death (Rom 8:6). Living by the Spirit is the only way our new self can overcome the desires of the flesh (Gal 5:16). Paul contrasts the natural consequences of each option: the fruit of the Spirit versus the deeds of the flesh (Gal 5:19–23).
When Paul addresses this theme in his letters, he highlights the now and “not yet” tension of the Christian life. The rebirth of our inner spiritual beings enables us to live for God as He intended. But since we continue to live in our earthly bodies, we continue to engage in the battle between flesh and spirit. The key to victory is walking in the Spirit, no longer obeying the desires of the flesh. If we allow our inner spirits to obey “the flesh,” we choose to allow sin to reign over us again (Rom 6:12–13). Paul offers us hope as we wait for the “not yet.” All of creation waits with us for the same restoration and fulfillment of God’s original intention (Rom 8:18–19).
Steven E. Runge, “Spirit and Flesh in Paul’s Letters,” in Faithlife Study Bible (Bellingham, WA: Lexham Press, 2012, 2016).