What do you let into your mind? What do you let settle itself down in your mind and make itself at home? What do you allow to take up residence in your mind so long that you find yourself meditating on it and allowing it to become a part of your character? 
How often do we let these sorts of things into our hearts: falsehoods, untruths, irreverence, mockery, injustice, prejudice, impurity, immorality, vileness, hatred, indecency, vulgarity, etc.? Honestly, do we let any of these in sometimes to find that they won’t leave? The items on this list were not chosen at random. They are actually the complete opposite of those things on which God tells us meditate. Think about this verse in light of these thoughts today: “Whatever things are true, whatever things are noble, whatever things are just, whatever things are pure, whatever things are lovely, whatever things are of good report, if there is any virtue and if there is anything praiseworthy–meditate on these things” (Phil. 4:8). What’s on your mind?