The Rishis of the Vedic Age explored the origin of conscious awareness which they experienced. Clearly the mind, the vital force and physical existence were not the “first movers”; they could not be the original cause, as they are all derivative and limited powers. Yet our powers of understanding, and our language to express any experience that transcended the framework of body, life and mind are limited. They therefore had to adopt “negative” forms to redirect the attention away from the outer forms that preoccupy our waking awareness. “Not this, not that” became a formula for this redirection of the attention.
The third verse of the Kena Upanishad takes up this issue of redirection away from the outer world to find the true source of all that here exists and that we can experience with our mind and senses:
“There sight travels not, nor speech, nor the mind. We know It not nor can distinguish how one should teach of It: for It is other than the known; It is there above the unknown. It is so we have heard from men of old who declared That to our understanding.”
Sri Aurobindo observes: “For behind all and dominating all that we become and experience, there is something that originates, uses, determines, enjoys, yet is not changed by its origination, not affected by its instruments, not determined by its determinations, not worked upon by its enjoyings. What that is, we cannot know unless we go behind the veil of our mental being which knows only what is affected, what is determined, what is worked upon, what is changed. The mind can only be aware of that as something which we indefinably are, not as something which it definably knows. For the moment our mentality tries to fix this something, it loses itself in the flux and the movement, grasps at parts, functions, fictions, appearances which it uses as planks of safety in the welter or tries to cut out a form from the infinite and say, ‘This is I.’ In the words of the Veda, ‘when the mind approaches That and studies it, That vanishes.’
“But behind the Mind is this other or Brahman-consciousness, Mind of our mind, Sense of our senses, Speech of our speech, Life of our life. Arriving at that, we arrive at Self; we can draw back from mind the image into Brahman the Reality.”
“Obviously, Brahman is not a thing subject to our mind, senses, speech or life-force; it is no object seen, heard, expressed, sensed, formed by thought, nor any state of body or mind that we become in the changing movement of the life. But the thought of the Upanishad attempts to awaken deeper echoes from our gulfs than this obvious denial of the mental and sensuous objectivity of the Brahman. It affirms that not only is it not an object of mind or a formation of life, but it is not even dependent on our mind, life and senses for the exercise of its lordship and activity.
Sri Aurobindo, The Upanishads, Kena Upanishad and analysis, pp. 101-102, 120-123