"For I feel a divine jealousy for you, since I betrothed you to one husband, to present you as a pure virgin to Christ. But I am afraid that as the serpent deceived Eve by his cunning, your thoughts will be led astray from a sincere and pure devotion to Christ." — 2 Corinthians 11:2-3
From the beginning, Satan has had a favorite target for his attack. We picture it being an all-out fierce battle, with fire and smoke and explosions and the like. However, he is much to cunning for that type of attack. In fact, most of his attack is not even a frontal attack. Like I just said, he is much to cunning and deceptive to just run straight at you with everything that he has. So, he goes a different route. He goes after that one thing in you that will affect every single thing that you will do in your life.
The serpent deceived Eve by playing with her thoughts. He does the same thing today. And do you know why? Because he's effective. This is why it is VITAL for all Christians to protect our minds so that we do not give the Enemy a foothold into our lives.
"Do not be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect." — Romans 12:2, ESV
Transformation comes by the renewal of our minds. Without that, transformation doesn't happen.
Are you getting time alone with the Holy Spirit? Are you getting time with him in the Bible, listening to what he says rather than what you think? What are you filling your mind with? Because the truth of the matter is this: if you do not control your mind and the thoughts that come, then your mind will control you.