The MIND. God gave us a mind for thought; it is part of the Soul area. The Soul is your mind, will and emotions. Your thoughts will control your will. When you don't want to do something but you know you should your minds tells your will to do it. When my kids were little I would tell them to set their will on wanting what I said was going to happen like you would change a dial on the stove to set the temp. Our mind/thoughts set the will.
Then there is the emotions. Someone says; I can't control my emotions. And they rant and rave and get angry or sad. But then there are people who work in the ER, or in war where their friends are killed, or an EMT who comes on the horrible scene of a wreck. They tell themselves (thoughts) stay focused for the task at hand. They can't fall apart or they can't help. So it all happens in the mind.
In 2 Corinthians 10:4-5 says that we can cast down strongholds, arguments and imaginations that don't line up with the Word of God and then take our thoughts into the captivity of Christ.
Think about what you think about and be sure your thoughts are in agreement with what God says. If not find the scripture you need and quote it, speak it out loud and even memorize it. Meditate on it. Let the Word of God be food to your mind and your soul would be stronger for it.