For the sinful nature desires what is contrary to the Spirit, and the Spirit what is contrary to the sinful nature. They are in conflict with each other, so that you do not do what you want.
- Galatians 5:17
Spirit vs. Sinful Nature
They are in conflict so that you do not do what you want to do.
Your sinful nature -
You naturally want to sin. Since the spirit of God that lives in you as a christian conflicts with that, and you follow that spirit, you shouldn't always do what you want. Eventually, what you want should match up with what God (the spirit) wants.
I want this.