For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right, but not the ability to carry it out.
Romans 14-17, about the sin struggle, is apparently so crucial and so surprising that Paul feels the need to reiterate his points. Verses 18-20 largely restate verses 14-17.
First of all Paul states: "For I know that nothing good dwells in me, that is, in my flesh." Paul is clarifying that when he says "nothing good dwells in me" he means in his flesh, that is, in his unredeemed, sinful tendency to resist God.
He goes on to say: "For I have the desire to do what is right, but not the ability to carry it out." The problem is that Paul lacks the power. He is admitting that he is powerless to win the battle. He is a bit like the alcoholic who says, "I am powerless and I need God for this battle." When it comes to sin, we are saying, "I am powerless and I need God to win this battle. I need the power of the Spirit." So that leads us to surrender, "Lord, I cannot do this, but you can. Lord, I depend upon you."
Paul's next statement, in 19, "For I do not do the good I want, but the evil I do not want is what I keep on doing," basically restates verse 15, "For I do not understand my own actions. For I do not do what I want, but I do the very thing I hate."
And then his next statement, verse 20, "Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me," largely reiterates verse 17, "So now it is no longer I who do it, but sin that dwells within me."
The distinction Paul makes here in verse 20 is important. "It is not me who sins. That is, it is not the real me, but it is the sin in me." Paul knows that as believers we have a new heart and deep down we want to live for Christ. That's the real me. The real me deeply desires to live a life of holiness and obedience and surrender to Jesus Christ. We are new creations in Christ, and that's who we really are. This tendency to sin is not the real us.
Lord, thank you that I'm a new creation and my deepest desire is to please you.