This Upanishad belongs to the Atharva Veda. As the name of the Upanishad suggests, the teachings revealed in it are such as to leave its students clean, like a shaven head (mundaka), rid of the veil of ignorance. The lucid translation of the text along with Shankaracharya's commentary on it is an additional aid to comprehend the profundity of the subject.
This world is nothing. It is at best only a hideous caricature, a shadow of the Real. We must go to the Real. Renunciation will take us to It. Renunciation is the very basis of our true life; every moment of goodness and real life that we enjoy is when we do not think of ourselves.
-Swami Vivekananda