A mind swept completely clean is easy prey to outside influence, either that of imperfect human instructors or, worse still, of superhuman demonic forces that, according to the Bible, are desirous of gaining mastery over man’s mind.​—1 Timothy 4:1; compare Luke 11:24-26.

It is just such a “swept clean” mind, not refilled with spiritually wholesome thoughts, that Jesus said would be occupied by demons.​—Luke 11:24-26.

Jesus Christ indicated this in saying that when an unclean spirit comes out of a man and later finds that “house” swept clean and adorned, “it goes its way and takes along seven different spirits more wicked than itself, and, after getting inside, they dwell there; and the final circumstances of that man become worse than the first.” (Luke 11:24-26)