The Mundaka Upanishad is complex and seems somewhat obscure to our modern understanding. It appears in the Atharva Veda, and thus represents one of the older streams of thought as presented by the Rishis to their posterity. Much of the obscurity is due to its treatment of various practices and sacrifices and its use of symbolic language to convey a meaning to those who had an existing familiarity with the specifics referred to. Yet within the Mundaka Upanishad one may still extract very substantial guidance for the seeker of knowledge of Brahman.
Sri Aurobindo has provided a translation on this Upanishad which helps to clarify otherwise difficult passages, but he has declined to provide any extensive commentary on the Upanishad itself.
Certain sections of this Upanishad contain passages that are important and rightfully famous in their explanations, such as the role of the syllable OM, or the passage about two birds sitting on a common tree. Both of these will be taken up in due course as the review of this Upanishad proceeds.
Given the obscurity of some passages related to specifics of various sacrificial practices of an ancient time, and their symbolic representations in terms of the spiritual practices of the aspirant, there is a certain range of interpretation possible, from those that exclusively dwell on the external aspects of the sacrifice, for instance, and those that relate them to inner spiritual experience. As with every text or scripture, there are elements which are temporary and temporal in nature, and others which remain true and valuable without regard to the temporal elements. It is these latter which we intend to highlight as our focus here.
The Mundaka Upanishad focuses attain on attaining to the Supreme Brahman and distinguishes the higher knowledge of the Supreme from the lower knowledge related to actions in the world. Its primary role is to focus the mind of the seeker on the Supreme in an exclusive concentration. In a world fixated on transitory things, such a focus is needed to break out of the bounds of body, life and mind.
Sri Aurobindo, The Upanishads, Mundaka Upanishad, pp. 193-210