Watchman Nee once wrote, "Man's will and spirit are like a citadel which the evil spirits crave to capture. The open field where the battle is waged for the seizure of the citadel is man's mind." (The Spiritual Man, Vol 3, page 7.)
Nee believed that man's spirit and his soul are two distinctly different functions of his personality. And he envisioned man's soul as made up of three major faculties: the mind, will and emotions.
It seems reasonable that the way to control a person's life is to capture his will, his volition. That's how Satan enslaved the whole human race... by bending Adam's will to the Satanic will. But how did he do it?
He did it by influencing Eve's, and then Adam's, mind. He inserted thoughts into their mental stream. He changed the atmosphere of their thinking processes. He captured their imagination by changing their thinking, therefore arresting their will.
After all, how do you change someone's mind? By changing their thinking. So, how do you change their thinking? By broadcasting thoughts that serve your purpose.
Control the thinking, and you control the will. Control the will, and the person begins to do your will. Now you see what Nee meant - the will is the citadel which the evil spirits crave to capture... so they can control the whole person.
So how does the believer keep that from happening? It's sometimes called "spiritual warfare" - fighting back against Satan's schemes by learning spiritual tactics that frustrate his efforts. (See Ephesians 6:10-18.)
And the first rule of spiritual warfare is to rely on God's weaponry, not ours.
The Apostle Paul said, "The weapons we fight with are not weapons of the world. On the contrary, they have divine power to demolish strongholds. We demolish arguments and every pretension that sets itself up against the knowledge of God, and we take captive every thought to make it obedient to Christ." (2 Corinthians 10:4-5 NIV.)
Taking "captive every thought" amounts to spiritual warfare over who owns your thinking. And you're in control over who owns your thinking.
"Put on the full armor of God so that you can take your stand against the devil's schemes... And pray in the Spirit on all occasions with all kinds of prayers and requests." (Ephesians 6:11,18 NIV.)