One of the key concepts of Hinduism is the belief in an ultimate reality called Brahman which is the source of all living things in this universe.
Brahman is the ground of all reality and existence. Brahman is uncreated, external, infinite and all-embracing. It is the ultimate cause and goal of all that exists. It is One and it is All. All beings emanate from
Brahman; all beings will return back to the same source. Brahman is in all things and it is the true Self (atman) of all beings.
Upanishads, the ancient scripture of Hinduism, teaches that the ultimate ground of the universe is one with the ground of the thinker himself. For instance Chandogya Upanishad suggested, "tat tvam asi" ('that art
thou' or "that is what you are.") expressing the identity of Brahman and the Self (atman).
"Now, the name of this Brahman is 'Real' (satyam). This word has three syllables: sa, ti, and yam. Of these, sat is the immortal, and ti is the mortal, while the syllable yam is what joins those two together. Because the two are joined together (yam) by it, it is called yam. Anyone who knows this goes to the heavenly world every single day."
- from the Chandogya Upanishad
He is the Supreme Brahman, the Self of all, the chief foundation of
this world, subtler than the subtle, eternal. That thou art; thou art
- Atharva Veda
He is the eternal Reality, sing the scriptures,
And the ground of existence.
Those who perceive him in every creature
Merge in him and are released from
The wheel of birth and death.
- Shvetashvatara Upanishad
In its deepest essence, the human soul is identical with the immortal Brahman that sustains the entire universe.
Bhagavad Gita says that "those who know the soul, are immortal."
I shall tell you of the soul. The soul is God who is immortal and infinite, who has no beginning and will have no end, and who both exists and does not exist. Those who know the soul, are immortal.
The soul dwells in every living being, and in every part of every living being; it dwells in the hand and the foot, the skull and the mouth, the eye and the ear. Although it does not itself have senses, it shines through every sense. It is completely independent, yet all beings depend on it.
The soul is both near every living being, and far from every being. The soul is both inside and outside every living being. The soul is the cause of movement, but does not itself move. The soul is one, yet has innumerable forms. The soul creates, preserves, and destroys.
The soul is the light of every light; and its light transcends the duality of brightness and darkness. The soul is the light of knowledge; and its light is also the goal of knowledge. In the soul the subject and object of knowledge are one.
Bhagavad Gita 13.12-17
Vedic literature suggests that there is a single essence (brahman) that underlies all existence and animates all living beings. A person's realization of the identity and unity of atman and brahman is believed to bring about liberation or
moksha. When that happens, he or she is freed from all restraints of the mind and body, and thereby transcends all distinctions. Both the Upanishads and later philosophy emphasize the role of jnana or knowledge in the attainment of moksha.
The concept that brahman and atman are ultimately the same is very difficult to understand. The Chandogya Upanishad, for example, compares the learning process to reach there to crossing the ocean of suffering. An person needs to meditate on the nature of the self to know brahman. Brahman cannot be defined according to Hindus, because to define brahman would mean limiting it. So we arrive at a paradoxical situation. C. Scott Littleton in Hinduism: The Sacred East described it this way:
"If brahman is indeed infinite and limitless, encompassing the variety of the whole world, then it must be the source of the universe, as the Chandogya Upanishad teaches. However, as the one true absolute, this same brahman is spoken of as remaining transcendent, beyond all differences. How, then, can such a single reality account for the diversity of the world? How can a single consciousness constitute the atman within different individuals without itself being divided?"
Philosophers wrestled with this question for centuries. A number of schools of thought exists that treat this differently. For example, the Vedanta school of philosophy upholds the doctrine of brahman as the ground of all being. But there is no agreement on the questions of the relation between the one brahman and the diversity of creation and, in particular, of the relation between the universal brahman and the individual atman. Individual souls are bound in misery, they maintained, because of the difference between brahman and atman. Tp them, this suffering is due to people's ignorance (called avidya) of the essential non-difference between brahman and atman.
Shankara, an 8th century hindu philosopher, believed that the ordinary world, as individuals perceive it, is essentially an illusion. On the level of ultimate reality, only brahman exists, and this undivided consciousness is the true identity of each individual. Shankara's stance is called advaita (non-dualism).
Others maintained that the distinction between god and god's devotees must be retained.
Ramanuja, an 11th century hindu philosopher, believed in the principle of vishishta dvaita (qualified non-dualism). According to Ramanuja, the individual soul is not identical with god. So, a devotee may worship god even after liberation or moksha. Moksha can be attained through bhakti (devotion), which involves the constant remembering of god or the surrender of the individual self to god.