The Upanishads declare: ~ “Neti Neti—not this, not this, not that.+

Rig Veda: ~ 'Prajnanam Brahma'- Consciousness is the ultimate reality or Brahman or God in truth. 

God in truth is the Atman, the Self. Atman is present in the form of consciousness.

Do not accept any other God other than Atman not worship other than Atman.

Let these words be inscribed in your subconscious.

Nothing is real but God. Nothing Matters but love for God in truth. God in truth is everywhere and in everything.

God in truth is hidden by the illusory universe. God in truth alone is and all else is an illusion.

Remember:~

Consciousness is within, the consciousness is without; the consciousness is before,  consciousness is behind;   consciousness is on the right,  consciousness is on the left;   consciousness is above and consciousness is below.  Consciousness is not an object, as it is invisible, beyond the reach of the physical eyes.  Consciousness is the ultimate truth. And the ultimate truth is Brahman or God in truth.

The world in which we exist is merely an illusion created out of consciousness.  Therefore, hold on to the consciousness which is real and eternal, and mentally negate the world in which we exist by realizing the world in which we exist is nothing but consciousness.   

Upanishads declare: ~ “Neti Neti—not this, not this, not that.” This does not mean that Brahman is a negative concept, or a metaphysical abstraction, or a nonentity, or a void. It is not another. It is all-full, infinite, changeless, Self-existent, Self-delight, Self-knowledge, and Self-bliss. It is the essence. It is the essence of the knower and the known.

Sage Sankara said: - The Brahman is impersonal, without Gunas or attributes (Nirguna), formless (Nirakara), (without special characteristics (Nirvisesha), immutable, eternal, and non-agent (Akarta). It is above all needs and desires. It is always the Witnessing Subject. It can never become an object as it is beyond the reach of the senses. Brahman is non-dual, one without a second. It has no other besides it. It is destitute of difference, either external or internal. Brahman cannot be described because description implies a distinction. Brahman cannot be distinguished from any other than it. In Brahman, there is not distinction between substance and attribute.

In Manduka Upanishad Brahman and Atman are defined as the same:~

सर्वं ह्येतद् ब्रह्मायमात्मा ब्रह्म सोयमात्मा चतुष्पात् / sarvam hyetad brahmaayamaatmaa brahm soyamaatmaa chatushpaat –

Mandukya Upanishad, verse-2

Translation:~

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

Fragmented Verse:

सर्वम् हि एतद् ब्रह्म अयम् आत्मा ब्रह्म सः अयम् आत्मा चतुस पात् / sarvam hi etad brahm ayama aatmaa brahm sah ayam aatmaa chatus paat

Simple Meaning:~ 

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 color red? Is any amount of thinking or reasoning on his part ever going to make him understand the sensation of the color 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 color red; those who can sense it cannot explain or argue with those who have never sensed it.

Bhagavad Gita:~ brahmano hi pratisthaham Brahman is considered the all-pervading consciousness which is the basis of all the animate and inanimate entities and material. (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, mantrams and meditation--all come from the Self.

So, it clearly says the one who meditates 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, mantrams 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, mantrams 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. :~Santthosh Kumaar