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.
If a person who lives in God becomes miserable, what is the use of living in God? What is the use of such a God? Throw such a God overboard into the Pacific Ocean. We do not want such a God!
-Swami Vivekananda