For the good that I would I do not: but the evil which I would not, that I do. Rom. 7:19.
Suppose I decide that I want to be a great singer. I rent a concert hall, and advertise in all the papers: "Come and hear the concert." I've made a good choice. I want to sing like one of the greats. Nothing wrong with that choice. So the crowd turns out. The time comes for the concert to begin. I go out onto the platform, and the piano gives the introduction. I open my mouth. To will is present with me, but now I've got to perform. And how to perform I find not! My voice squeaks and cracks and fades away, and above the shouts of laughter and derision, I make my way offstage. I have chosen to be a great singer, but I can't perform.
Suppose I choose to live the Christian life. Nothing wrong with that choice. I watch to see how it's done, and then I try. But although I've made the right choice, when it comes to performing, I'm finished. Paul discovered the same thing. Even Paul, with his tremendous intellect, who apparently was such a strong person, had discovered his weakness within. He knew the right choices, and he chose correctly--but then he couldn't perform. He talks about it in Romans 7. Right in the middle of his frustration, expressed by all those would nots and do nots, we find this verse, "For I know that in me (that is, in my flesh), dwelleth no good thing: for to will is present with me; but how to perform that which is good I find not" (verse 28).
When I decide that I want to do right, that I would like to keep God's commandments and be obedient to Him, I've made the right choice. But if I'm trying to fight sin and the devil myself, I can never succeed, because the problem of sin is on the inside, and even strong people can control only the externals.
In order to have the proper understanding of how to use your will (your power of choice), and your willpower (your power to follow through with your choice), you must understand the role of human effort in living the Christian life. God has never promised to seek Himself for us. He has never promised to do our Bible study and our prayers and our witnessing for us. But He has promised to fight Satan for us (see Rom. 8:37). As we put forth our effort toward knowing Him, He will give us victory.