All should guard the senses, lest Satan gain victory over them; for these are the avenues of the soul. CCh 166.1
You will have to become a faithful sentinel over your eyes, ears, and all your senses if you would control your mind and prevent vain and corrupt thoughts from staining your soul. The power of grace alone can accomplish this most desirable work. CCh 166.2
Satan and his angels are busy creating a paralyzed condition of the senses so that cautions, warnings, and reproofs shall not be heard; or, if heard, that they shall not take effect upon the heart and reform the life. CCh 166.3