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.
May I be born again and again, and suffer thousands of miseries so that I may worship the only God that exists, the only God I believe in, the sum total of all souls--and, above all, my God the wicked, my God the miserable, my God the poor of all races, of all species, is the special object of my worship.
-Swami Vivekananda