Sri Aurobindo translates Mandukya Upanishad, Verse 7: “He who is neither inward-wise, nor outward-wise, nor both inward- and outward-wise, nor wisdom self-gathered, nor possessed of wisdom, nor unpossessed of wisdom, He Who is unseen and incommunicable, unseizable, featureless, unthinkable, and unnameable, Whose essentiality is awareness of the Self in its single existence, in Whom all phenomena dissolve, Who is Calm, Who is Good, Who is the One than Whom there is no other, Him they deem the fourth: He is the Self, He is the object of Knowledge.”
The sages speak of a state of awareness that is pure existence, that is not defined by any particular characteristic, which would be limiting to it, but is not also restricted by the negative descriptions they use to avoid limitation. The “not this, not that” descriptions are intended for the mind to ensure that it does not try to fixate on one particular attribute or state of awareness and thereby try to define the Absolute consciousness. The other side of this is the statement “All this is the Brahman”, which encompasses all, again, without limiting the Supreme even by the totality of all the manifested universe.
The initial descriptions here ensure that the seeker does not focus solely on the dream state, the waking state or the state of deep sleep. The status of pure Existence is one which we find impossible to conceptualize until the actual experience occurs. It is this experience, which some call Nirvikalpa Samadhi, the Samadhi “without seed”, that is so overpowering, that those who gain even a taste of it are often tempted to renounce all outer forms and actions in order to live in that transcendent yet all-embracing experience of pure Existence.
The sage makes it clear that this is the Eternal which encompasses and transcends and embodies all that exists in the manifested universe.
Sri Aurobindo, The Upanishads, Mandukya Upanishad, pp.319-321