Mundaka-2-1-4-agnīrmūrdhā

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

Com.—This text is intended to show that the virat purusha within the globe, who is born of Hiranyagarbha the first born, is born only and a modification, of this purusha, though apparently distanced by an intermediate principle. The text also describes him. ‘Agnihi,’ the devaloka or svarga, from the Sruti ‘This loka verily is Agni, O Gautama.’ ‘Murdha,’ head; whose eyes are the sun and the moon. The word ‘yasya’ (of whom) should be read in every clause. The word ‘asya’ subsequently occurring being converted into ‘yasya’ whose speech are the opened, i.e., celebrated Vedas. ‘Hridayam’ heart. ‘Visvam,’ the whole universe. The whole universe is only a modification of the mind for it is absorbed into the mind during sleep and because it issues from the mind when waking, like sparks of fire and from whose feet the earth was born; this deity, all-pervading, endless, the first embodied existence having for its body the three lokas is the interior atman of all created things; for, it is he who, in all created things, is the seer, the hearer, the thinker, the knower and who is the cause of all. It is next stated that all living beings who come into samsara through the five fires are also born of the same purusha.

Links
Various resources on the Mundakopanishad
Upanishad Series – Mundakopanishad Commentary by Swami Chinmayananda