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.
I am the thread that runs through all these pearls, and each pearl is a religion or even a sect thereof. Such are the different pearls, and God is the thread that runs through all of them; most people, however, are entirely unconscious of it.
-Swami Vivekananda