So I find it to be a law that when I want to do right, evil lies close at hand. For I delight in the law of God, in my inner being, but I see in my members another law waging war against the law of my mind and making me captive to the law of sin that dwells in my members. Wretched man that I am! Who will deliver me from this body of death? (Romans 7:21-24)What, then, is his answer?
Thanks be to God through Jesus Christ our Lord! So then, I myself serve the law of God with my mind, but with my flesh I serve the law of sin (Romans 7:25)Is he resigning himself to sinning with his flesh? No! He has already emphasized that we ought not sin. So what is he saying? "Who will deliver me from this body of sin and death? Thanks be to God through Jesus Christ our Lord!" So Christ is our deliverer, and we will do what it is we can do, though it is very little, leaving the rest to God through Jesus Christ whom Paul implies is the one who will deliver him from this body of death. So in those places where I am able to serve the law of God, I do, and where I cannot, I don't.
In chapter 8 this is explained: In Christ we are not condemned because in him the law of the Spirit of life has set us free from the law of sin and death. God did what the law could not--he condemned sin in the flesh. Thus the requirement of the law is fulfilled in us who walk according to the spirit. Then he returns to the mind:
For those who live according to the flesh set their minds on the things of the flesh, but those who live according to the Spirit set their minds on the things of the Spirit. (Romans 8:5)So if we walk in the Spirit, then we set our minds on the things of the spirit. And Paul says that he serves the law of God with his mind. Thus he walks by the Spirit. That is to say that, though he sins, his life his characterized by the thoughts that proceed from the Spirit. Perhaps these thoughts change him over time, but the point is not the change, but the glory of God that may be shown forth in that change. That is why it is the power of the Spirit that we rely on for sanctification, just as we were saved by the uniting of ourselves to Christ by the Spirit.
The Spirit has power which no person has to change people. We can think thoughts without changing, but we cannot have thoughts impelled into our very natures by the Spirit without changing. People argue, but all they can change are peoples' thoughts. The Spirit changes how people think and what they think about, changing our natures from death to spiritual life.