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.
Look here -- we shall die! Bear this in mind always, and then the spirit within will wake up. Then meanness will vanish from you, practicality in work will come, you will get new vigor in mind and body, and those who come in contact with you will also feel that they have really got something uplifting from you.
-Swami Vivekananda