A good introduction is an answer by Zen master Bankei (1622–1693) to a question about meditation: “My mind is constantly filled with thoughts. No sooner do I get rid of one than another arises. How can I clear my mind of these?” Bankei responded: “To try to rid the mind of thoughts by effort is like trying to wash away blood with more blood. What you must realize, is that the Unborn Buddha-mind is free of illusion. It’s because you think your thoughts are something real, that you are caught up in them. Just understand that they are unreal, ephemeral apparitions that arise and pass away. Don’t seize them or reject them; let them be. They’re like the images reflected in a mirror. The mirror itself is empty but reflects whatever is placed before it. Nor does the image leave a stain on the mirror. When the object is removed, the mirror is empty and bright once again. The Unborn Buddha-mind is much brighter than any mirror.”
"The Great World History Book"