Many years ago, one night I walked down to the shallow portion of the stream beside my run down old ranch house. I could see countless moons in the water. Then I thought to myself that this might make a good koan. Which one is the real moon? This for me is like saying which of my thoughts is the pure Mind? From this, I mused just how close 'pure Moon thought' and pure Mind are, so close, as to mistake thought for pure Mind.
Back to the moons in the water, if someone who had never before seen the moon above, in the cool night sky, were to check out all of these moons, looking for the exact right one, he would go mad. This would be a real fool's errand. I think you can guess where I am going with this. Our thoughts about pure Mind, while being copies or reflections of it, are not the same thing—not even close. Still, like our fool we follow the stream, especially its wide shallow places where many more moons appear, and look for the real moon. Then there are those who would declare all the moons are the real moons! But then during July, when most of the stream dries up, where did all the moons go?
There is no adequate way to describe by words the difference between the thought of pure Mind and pure Mind, itself, or the difference between moons in the water and the real moon overhead. Words are not all that adequate. Saying fire can't give us fire on a cold night no matter how many times we say fire. And if we think about pure Mind for days and months we won't get any closer to pure Mind, itself. Something else has to happen. This something else is where Zen steps in or I should say gives the seeker some sound advice.
Such advise is meant to urge the seeker to go much deeper than just stopping at thoughts and concepts. Don't spend your time chasing the conditioned; trying to forge it into your true, unconditioned nature, deceiving yourself by doing so. Zen is something like when the pure subject meets the pure object, face to face—something like flint and steel making a spark. Notice, that I said "pure" not just the meeting of subject and object. The pure subject is presuppositionless. The pure object is beyond the sense fields including our mental images. Only in this way is it possible to realize pure Mind, seeing for the first time what our thoughts and concepts are made of.