Mark 7:20-23 And then he added, "It is the thought life that defiles you. For from within, out of a person's heart, come evil thoughts, sexual immorality, theft, murder, adultery, greed, wickedness, deceit, eagerness from lustful pleasure, envy, slander, pride, and foolishness. All these vile things come from within; they are what defile you and make you unacceptable to God."
This is one truth that I have found to be very hard to deal with. God knows my every thought. I have to admit that sometimes I am not too proud of what I think about. It makes me uncomfortable to know that God knows what I am thinking. Some things that I think about would I would never act out in my life; nevertheless, they are there and if I allow them to stay there they do affect me. I am thankful that my thought life doesn't control me, but it can.
The more we think about something, the easier it becomes for it to control us and determine our behavior. Who we become in life is directly linked to what we allow ourselves to dwell on. It is our responsibility to take control of our thinking. We can resist the urge to react according to the thoughts that cross our minds. How? By letting Christ be Lord of our lives.
When Jesus is in charge and takes control of our hearts, He takes control of our minds as well. He has the power to keep our thought lives in check. The more He is Lord of our lives, the less we lose control of our minds.
If you are having trouble controlling your thought life, I urge you to let the Lord be your Lord. Let Him take charge of it. Let Him help you to not become defiled by your thoughts.. It does not mean you will never have another unholy thought, but it does mean you will not dwell on it to the point of becoming a slave to it. It will not lead you into sin.