Mandukya Upanishad, verse-2
sarvam(सर्वम्)- Whole/All/Everything; hi(हि)- Really/Just/Surely/Indeed;etad(एतद्)- This here/This; brahm(ब्रह्म)- Brahm/Brahman;ayam(अयम्)- This/Here; aatmaa(आत्मा)- Atma/Atman; sah(सः)- He;ayam(अयम्)- This/Here; chatus(चतुस्)- Four/Quadruple; paat(पात्)- Step/Foot/Quarter
सर्वम् हि एतद् ब्रह्म अयम् आत्मा ब्रह्म सः अयम् आत्मा चतुस पात् / sarvam hi etad brahm ayama aatmaa brahm sah ayam aatmaa chatus paat
All indeed is this Brahman; This Atman is Brahman; He, this Atman has four steps/quarters.
While Brahman lies behind the sum total of the objective universe, some human minds boggle at any attempt to explain it with only the tools provided by reason. Brahman is beyond the senses, beyond the mind, beyond intelligence, beyond imagination. Indeed, the highest idea is that Brahman is beyond both existence and non-existence, transcending and including time, causation and space, and thus can never be known in the same material sense as one traditionally 'understands' a given concept or object.
Imagine a person who is blind from birth and has not seen anything. Is it possible for us to explain to him the meaning of the colour red. Is any amount of thinking or reasoning on his part ever going to make him understand the sensation of the colour red? In a similar fashion the idea of Brahman cannot be explained or understood through material reasoning or any form of human communication. Brahman is like the colour red; those who can sense it cannot explain or argue with those who have never sensed it.
Brahman is considered the all-pervading consciousness which is the basis of all the animate and inanimate entities and material. (brahmano hi pratisthaham, Bhagavad Gita 14.27)
In Advaita Vedanta: - Brahman is without attributes and strictly impersonal. It can be best described as infinite Being, infinite Consciousness and infinite Bliss. It is pure knowledge itself, similar to a source of infinite radiance. Since the Advaitins regard Brahman to be the Ultimate Truth, so in comparison to Brahman, every other thing, including the material world, its distinctness, the individuality of the living creatures and even Ishvara (the Supreme Lord) itself are all untrue. Brahman is the effulgent cause of everything that exists and can possibly exist. Since it is beyond human comprehension, it is without any attributes, for assigning attributes to it would be distorting the true nature of Brahman. Advaitins believe in the existence of both Saguna Brahman and Nirguna Brahman; however they consider Nirguna Brahman to be the absolute supreme truth.
Chandogya Upanishad:- One who meditates upon and realizes the self discovers that everything in the cosmos-- energy and space, fire and water, name and form, birth and death, mind and will, word and deed, mantram and meditation--all come from the Self.
So, it clearly says the one who meditate upon the self (consciousness) discovers that everything in the cosmos-- energy and space, fire and water, name and form, birth and death, mind and will, word and deed, mantram and meditation--all come from the Self. Therefore , there is a need to know the fact that ,the true self is not physical but the soul in order to realize the fact that : the cosmos-- energy and space, fire and water, name and form, birth and death, mind and will, word and deed, mantram and meditation--all come from the Self, which is in the form of consciousness.
Atman is Brahman. Brahman the Absolute is alone real; this waking is unreal; and the three states are non-different from Brahman.