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.
Those who grumble at the little thing that has fallen to their lot to do will grumble at everything. Always grumbling, they will lead a miserable life, and everything will be a failure. But those who do their duties as they go, putting their shoulders to the wheel, will see the light, and higher duties will fall to their share.
-Swami Vivekananda