The Vedas exclaim from time immemorial, Ekam Sat Vipra Bahudha Vadanti, Existence is One, Sages call it by different Names Rig Veda, 1-164-146. God, Brahman, Allah, Isvara, Jehovah, Ahuramazda, etc., are one. I offer my worship to that Supreme Being the One eternal homogeneous essence, indivisible mass of bliss and intelligence whom sages describe in a variety of ways through diversity of intellect.
In the beginning Brahman who is One without a second alone existed. When darkness was rolling over darkness there was Existence only. Nobody knows how this universe came into being. You will find in Rig Ved: Who knows here, who can here state whence came all this multifarious Universe? Even the Devas are posterior to its creation, who then knows whence this came out? Rig Veda VIII-17-6.
Atman alone exists. It appears as the objects which we cognise just as a rope appears as a serpent. Atman puts on the appearance of these phenomenal objects. That Brahman is the Self within all beings. That Brahman is without cause and without effect, without anything inside or outside, without defect or impurity, without length or breadth, without colour, shape or form. That Brahman is without limbs, parts, without name or caste, without hands and legs. That Brahman is an embodiment of wisdom, peace and bliss. It shines by Itself. It is self-luminous. All the objects that you cognise outside really exist in the highest Self. All the objects shine after them i.e., they borrow their light from the self-effulgent Atman. The whole world exists within Brahman. It appears as external through the force of Maya, just as your body appears in a mirror.
How can one describe the glory and greatness of the Brahman! Even the Vedas have sung in praise of Him according to their limited capacity. No one has been able to find out His beginning or end. He walks without feet, grasps without hands, hears without ears, sees without eyes, tastes without a tongue, smells without a nose, feels without a skin, talks without a mouth, because He is a mass of pure Consciousness. He is all-pervading. He has hands, feet, eyes, heads, faces everywhere. He is a wonderful entity. He is beyond the reach of mind and speech. You cannot see Him with these physical eyes, but you can realise Him with the help of your pure sharp, subtle intellect after purging the mind of all evil tendencies.
The eye cannot perceive Him. The mind cannot reach Him. The gross worldly intellect cannot grasp Him. The speech cannot describe Him. The speech returns back along with the mind, as it is not able to describe Him in adequate terms. We are baffled in our attempts to describe Him; His glory is indescribable. To describe Him is to deny Him. How can a finite mind grasp the Infinite? But He can be directly realised by that aspirant who is equipped with the four means of salvation, who does constant meditation, who has a sharp, pure intellect.
Saints emphatically declare that Brahman or the Eternal is That which is above the undifferentiated, That which is unborn either as cause or effect, That from which speech and mind turn back baffled, That which is not this, not that, Neti, Neti, etc. He is the real unconditioned Sat. He is the reality of realities (Satyasya Satyam).
Brahman is a mass of intelligence (Chidghana, Vijnanaghana, Prajanaghana). He is destitute of any other characteristics. He is entirely without any sort of difference. In Brihadaranyaka Upanishad IV-13, you will find: As a mass of salt has neither inside nor outside, but is entirely a mass of taste, thus indeed, has that Self neither inside nor outside but is altogether a mass of Knowledge. Just as a lump of salt has inside as well as outside one and the same saltish taste, not any other taste, so also that Brahman has inside as well as outside one and the same intelligence. Inside and outside are mental creation only. When the mind melts in silence, ideas of inside and outside vanish. The sage cognises one illimitable, homogeneous mass of consciousness only.
Akasa or ether is subtle, all-pervading and unattached. So it is compared to the Brahman. Srutis emphatically declare: Akasavat Sarvagata Nitya i.e., like ether all-pervading and eternal. If the pot is broken the pot-ether is not in any way affected. So it is unattached (Asanga).
Just as a house exists for somebody's use, so also the ears, eyes, hands, legs exist for the use of the Director of the ears, eyes, etc., who is entirely distinct from the ears etc. That Director is the real infinite I. He is the Inner Ruler. He is Immortal. He is pure consciousness. The capability of the ears to hear sounds, of the eyes to cognise objects depends upon the intelligence of this Director. Just as the moon borrows its light from the Sun, these senses borrow their lights, intelligence and power from the source, viz., Atman, who is the Director. Therefore it is quite appropriate to say that the Atman is the Ear of ears, Eye of eyes, Prana of Pranas, Mind of minds.
Atman is different from the knowable. He is beyond the unknowable also. He is incomprehensible. This does not mean that He is a non-entity or void or a negative concept, or a metaphysical abstraction. He is a mass of knowledge or pure consciousness. Consciousness is denser than stone or platinum or gold. He is the only real living entity, the substratum for everything.