Sri Aurobindo translates Shwetashwatara Upanishad, Chapter Six, Verse 17: “Lo, He is Immortal because He is utter existence; but He houseth Himself in the Lord and is the Knower, the Omnipresent that standeth on guard over this His universe, (Or, He is purely Himself, for He is the Immortal manifested in the Mighty One and becometh the Knower who reacheth everywhere and guardeth His cosmos,) yea, He ruleth all this moving world for ever and for ever, and there is no other source of greatness and lordship.
The Rishi here distinguishes various aspects of the One Eternal which later became more defined in Indian philosophy. The Eternal is without limits, immortal, unencumbered with attributes, free and unbound by any specific form. This does not imply that the Eternal is limited by this “freedom”. The Eternal also can take on the attributes of existence, including the status of Lord and Witness of the creation, both manifesting and controlling it, and observing it in action in all of its forms, beings, and interactions and events.
The Bhagavad Gita explains that there is the Kshara Purusha, the Immanent Witness in the individual beings and forms being manifested; there is also the Akshara Purusha that is not involved in the actions or the beings, but acts as a silent consenting witness to the action of Nature, Prakriti, and then there is the Purushottama, the Supreme Purusha which incorporates both the involved and the uninvolved statuses in a transcendent standpoint, not bound by either, but not separate either.
Once again, the mind does not easily reconcile what appears to it to be contradictions. This is the Upanishad’s attempt to explain “One without a Second” and “All This is the Brahman” in terms of the various standpoints and statuses that are operative.
Sri Aurobindo, The Upanishads, Shwetashwatara Upanishad, pp.369-384