Mahavakyas are the grand utterances of the Upanishads. They contain the essence of the Vedanta and the ultimate truth.
The Mahavakyas are:
- prajñānam brahma - "Consciousness is Brahman" Aitareya Upanishad
- ayam ātmā brahma - "This Self (Atman) is Brahman" Mandukya Upanishad
- tat tvam asi - "Thou art That" Chandogya Upanishad
- aham brahmāsmi - "I am Brahman" Brhadaranyaka Upanishad.
Kanchi Paramacharya, in reference to the four Mahavakyas.
Tat Tvam Asi, one of the Mahavakyasm, Vedanta.
The self in its pure and original condition - is completely or partially identical with the "Ultimate Reality", the ground and cause of all phenomena. The knowledge (jnana) determines the experience of Moksha (liberation) or healing that accompanies the mystical union.
Another interpretation is expressed that the outside world is identical with the ego. (Wikipedia)
The three main Vedantic directions:
• The Advaita in essence translated as "That," which refers to the ultimate reality (Brahman), and 'tvam' (the individual self jiva) as exactly the same.
• The Vishishtadvaita is 'that', the individual self, as part of the whole.
• The Dvaita interpretation 'atat tvam asi', meaning "You are not that". It is practiced as "Neti, neti", that means 'not this, not that'.
"This atman, which dwells in the heart, is smaller than a grain of rice, smaller than a grain of barely, smaller than a grain of mustard, smaller than a grain of millet, smaller than the germ which is in the grain of millet; this atman, which dwells in the heart, is also greater than the earth [the sphere of gross manifestation], greater than the atmosphere [the sphere of subtle manifestation], greater than the sky [the sphere of formless manifestation], greater than all the worlds together [that is, beyond all manifestation, being the unconditioned]." Chandogya Upanishad (Wikipedia)
God is bigger than the biggest and smaller than the smallest, Atman the indweller of the heart.
