The concept of Brahman?
The word 'brahman' is a noun in Sanskrit, in the neuter gender, not to be confused with the masculine noun 'brahmA' which is the name of the first of the triad of personal Gods: brahmA, viShNu and shiva. Nor to be confused with bhrama, meaning complexity, error or mistake. 'brahman' originates from the root verb 'bRRih' to grow or enlarge.
In the 'Taittariya Upanishad' II.1, Brahman is described in the following manner:
"satyam jnanam anantam brahma",
"Brahman is of the nature of truth, knowledge and infinity."
Infinite positive qualities and states have their existence secured solely by virtue of Brahman's very reality. Brahman is a necessary reality, eternal (i.e., beyond the purview of temporality), fully independent, non-contingent, and the source and ground of all things. Brahman is both immanently present in the realm of materiality, interpenetrating the whole of reality as the sustaining essence that gives it structure, meaning and existential being, yet Brahman is simultaneously the transcendent origin of all things (thus, panentheistic).
Several great sayings, indicate what the principle of Brahman is:
"Brahman is knowledge"- Aitareya Upanishad 3.3
ayam ātmā brahma
"The Self (or the Soul) is Brahman" - Brihadaranyaka Upanishad 4.4.5,
"I am Brahman"- Brihadaranyaka Upanishad 1.4.10
tat tvam asi
"You are that"- Chhāndogya Upanishad 6.8.7
sarvam khalv idam brahma
"All this that we see in the world is Brahman"- Madhavacarya, Mayavada sata dushani, text 6
"Brahman is existence, consciousness, and happiness" -Chhāndogya Upanishad 3.14.1
The description of Brahman from Mandukya Upanishad:
सर्वं ह्येतद् ब्रह्मायमात्मा ब्रह्म सोयमात्मा चतुष्पात्
sarvam hyetad brahmāyamātmā brahma soyamātmā chatushpāt
All indeed is this Brahman; He is Atman; He has four steps/quarters. - Verse-2
Thus, Brahman is conceived of as the very essence of existence and knowledge, which pervades the entire universe, including every living being. The goal of Hinduism is to somehow "wake up," and realize one's own connection to the divine reality that may be called Brahman or God.
All our knowledge of brahman comes from the scriptures and so is indirect (Sanskrit: 'parokSha'). It is however known, as direct (Sanskrit: 'aparokSha') knowledge by realisation and insight, once everything that is transient is transcended. It is not known otherwise; it is that which makes known what is known. By itself it is not an object of knowledge to be known. It is the very Consciousness (Sanskrit: 'cit', also 'caitanyaM') that cognises knowledge. There is no higher Reality outside that. Knowledge of absence of Consciousness implies the existence of Consciousness. While everything is presented to Consciousness, the nature of Consciousness is to be its own light. A lighted lamp needs no other light to illumine it.
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.