Doing what is good. Doing what is the will of God. This is what I want to do. I want to do what is good; I want to serve God. I want to obey all the commandments of God. I want to be a true disciple of Jesus Christ. I want to do everything that he asks me to do. This is what I have in my mind. This is what I decided to do.
But there is always a restraining force in my flesh that doesn't allow me to serve and obey God the way I want. This is the same thing that the Apostle Paul was talking about. We have a good mind to do what is good but the nature of sin in us would not allow us to do that good work. This is why some people are struggling with sin. Some people find it difficult to stop committing sin because the sinful nature always works against what is the way of God. We do not have the power in ourselves to do good except by the ability of the Holy Spirit.