"O wretched man that I am!  Who will hereafter deliver me out of the body of this death"  (Rom. 7:24, Expanded Greek Translation – EGT).

Paul is not discussing a new believer in Romans 7:7-25. Paul is not talking here about the struggle of two (2) natures, for at the Spirit birthing the old sin nature was exchanged for the new Christ nature. As a mature believer, Paul is discussing his own struggle between the unrenewed mind that operates out of the knowledge of good and evil, and the renewed mind that operates with the Spirit of Christ within us. Why do unbelievers sin? It is their nature to sin. Why do believers sin? They choose to, by choosing not to let the Holy Spirit renew their mind. They choose to, by not believing and letting Christ live His life of obedience in and through them.

Spirit birthed sons still have an unrenewed mind that focuses in on fleshly, temporal, or earthly things. Our earthly body is still here that can express these things of the unrenewed mind should we chose to obey that unrenewed mind that is contrary to the Spirit of God (Rom. 8:7). The unrenewed mind with corresponding body expression is defined as "the body of sin" (Rom. 6:6). "Knowing continually this, that our old man was once then co-crucified with Him, in order that the body of sin might once then be rendered powerless, that we are to no longer continually serve sin" (Rom. 6:6, expanded Greek translation). The old man and the original sin of Adam, with all of its spiritual consequences, were put to death upon the cross with Christ. This is so the body of sin might be rendered powerless, down from work, or unemployed.  Without a renewed and obedient mind, the body of sin will be re-employed in us. We still have a temporal earthly body and it will not be exchanged to a glorified body until one split second after death (II Cor. 5:1-4). Our temporal earthly mind was not put to death on the cross either, but is being renewed or exchanged throughout life by the Holy Spirit. Operating out of the unrenewed mind, we can still express sin and death.