“Do not conform to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God's will is -- His good, pleasing and perfect will.” (Romans 12:2 NIV)
How we act will be determined by how we think. If God is to change our lives, He must first change our minds. The human mind cannot be a vacuum. It will be filled either with good or evil. It will be filled either with Christ or with carnality. What will make the difference? It depends on us, and on what we allow to enter our minds. Negatively, our minds must be turned away from evil. We must be careful what kind of [things we watch on the screen], what kind of books we read, the things that occupy our thoughts. But it isn’t enough to put bad thoughts out of our minds. Positively, they must be replaced with good thoughts -- thoughts that are shaped by God and His word, by prayer.
-- Billy Graham in “Hope for Each Day: Words of Wisdom and Faith”