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.
Learning and wisdom are superfluities, the surface glitter merely, but it is the heart that is the seat of all power. It is not in the brain but in the heart that the Atman, possessed of knowledge, power, and activity, has its seat.
-Swami Vivekananda