“Free will is the ability to choose.” No, it’s not. The ability to choose only shows you have a will. Your will might be free, or it might not be.
Looking at the diagram above, suppose you choose option A. There is a reason you chose A, and that reason was determined by one of the preceding desires. You don’t choose your desires, at least not in the moment of choice. You can shape your desires over time through ongoing actions, but in the immediate moment of choice your strongest desire will determine which option you chose.
Your desires may be evil, and if they are, you will choose to do evil things. You may have good desires and evil desires. If so, the strongest of those desires will determine your choices.
If a man’s desires are only evil, all he can do is chose to act on one of those evil desires: the one which appeals to him most in the moment. This man is not able to chose good. He is a slave to evil.
If a man has good and evil desires, the potential to do good and evil is present, but he will still act out his strongest desire in the moment.
If a man has only good desires, all his choices will be good. This man is free.
Only through Christ can you become one who desires only the good. It is a process of a series of deaths and resurrections. It is not easy and is sometimes painful, but it is necessary.
“Do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what is that good and acceptable and perfect will of God.” ~Roman 12:2