"We make a vessel from a lump of clay;
It is the empty space within the vessel that makes it useful.
We make doors and windows for a room;
But it is these empty spaces that makes the room livable." -Tao Te Ching 11
It appears that many Christians today still believe meditation is "praying to the devil", or allowing demons to enter your mind etc. Well, if the mind is always occupied with thoughts, or if it isn't open to external input, what allows room for Christian teachings to enter, or the holy spirit for that matter?
There is something called working memory, which is a "space" that temorarily holds information which you are processing with your mind. Of course, if you are always hanging on to your opinions and beliefs, it's probable that even this little bit of space is not available. A person might be full of thoughts which they think is right and correct, and although it is unlikely that a person is 100% wrong about everything, what we do know is that regardless of the validity of their beliefs, what they are full of is their own opinions - or, if you will, full of themselves.