There are over 200 Upanishads but only 12 are considered as principal Upanishads. The names of the principal Upanishads are: Isa, Kena, Katha, Prasna, Mundaka, Mandukya, Taittiriya, Aitareya, Chandogya, Brhadaranyaka, Svetasvatara and Kausitaki. Adi Shankara has written commentaries on 11 of the Upanishads.

“From every sentence (of the Upanishads) deep, original and sublime thoughts arise, and the whole is pervaded by a high and holy and earnest spirit…In the whole world there is no study so beneficial and so elevating as that of the Upanishads. They are destined sooner or later to become the faith of the people.”

— Arthur Schopenhauer (1788-1860) German philosopher and writer. He was one of the greatest philosophers of the 19th century.

The Upanishads, along with the Bgagavad Gita and the Brahma Sutras, constitute the triple canon — the prasthana traya – of the spiritual tradition of India. According to Swami Vivekananda, “The essence of the knowledge of the Vedas was called by the name of Vedanta, which comprises the Upanishads….Strength, strength is what the Upanishads speak to me from every page. Therein lies strength enough to invigorate the whole world. They will call with trumpet voice upon the weak, the miserable, and the downtrodden of all races, all creeds, and all sects, to stand on their feet and be free. Freedom, physical freedom, mental freedom, and spiritual freedom are the watchwords of the Upanishads. The Upanishads are the Bible of India.”

“The Upanishads represent a great chapter in the history of the human spirit and have dominated Indian Philosophy ,religion and life for three thousand years. Every subsequent religious movement has had to show itself to be in accord with their philosophical statements. The Upanishads have shown an unparalleled variety of appeal during these long centuries and have been admired by different people, for different reasons, at different periods. They are said to provide us with a complete chart of the unseen Reality, to give us the most immediate, intimate and convincing light on the secret of human existence, to formulate, in Deussen’s words, ‘philosophical conceptions unequalled in India or perhaps anywhere else in the world,’ or to tackle every fundamental problem of philosophy. If the ideas of the Upanishads help us to rise above the glamour of the fleshly life, it is because their authors, pure of soul, ever striving towards the divine, reveal to us their pictures of the splendours of the unseen. The Upanishads are respected not because they are a part of sruti or revealed literature and so hold a reserved position but because they have inspired generations of Indians with vision and strength by their inexhaustible significance and spiritual power. Indian thought has constantly turned to these scriptures for fresh illumination and spiritual recovery or recommencement, and not in vain. The fire still burns bright on their altars. Their light is for the seeing eye and their message is for the seeker after truth. The treatises that deal with brahma-knowledge are called the Upanishads and so pass for the Vedanta.”
…… S . Radhakrishnan

Maharshi Aurobindo considered Upanishads as “the supreme work of the Indian mind”.

According to Adi Shankaracharya, the sole purpose of the Upanishads is to prove the reality of Brahman and unreality of the phenomenal universe of names and forms, and to establish the absolute oneness of the embodied soul and Brahman.

One of the greatest teachings of the Upanishads is that atman and Brahman are made of the same substance. When a person achieves moksha or liberation, atman returns to Brahman, to the source, like a drop of water returning to the ocean. The Upanishads claim that it is an illusion that we are all separate: with this realization we can be freed from ego, from reincarnation and from the suffering we experience during our existence. Moksha, in a sense, means to be reabsorbed into Brahman, into the great Universal Soul.

According to the Mundaka Upanishad, one should acquire two forms of knowledge: the apara (lower) and the Para (Higher). The lower consists of the four Vedas (that is to say, their ritualistic portions) and their six auxiliaries. It deals with the phenomenal universe. It is conducive to a man’s material welfare; but its results are impermanent.

The Higher Knowledge ( para vidya) is that by which the Imperishable Substance is known. This Imperishable Substance was given the name of Brahman by the ancient seers; hence the Higher Knowledge was also called Brahmavidya, the Knowledge of Brahman; and this is the knowledge to which was given the general name Upanishad. Brahmavidya was regarded as the foundation of all other forms of knowledge—sarvavidyapratishiha.

Greatest Statements (Mahavakyas) of the Upanishads

तत् त्वम् असि

“That Thou are”

Sanskrit : Tatvam asi { Chandogya Upanishad 6}

अयम् आत्मा ब्रह्म

“The Self (the Soul) is Brahman.”

Sanskrit: aham brahmasmi. (Brihadaranyaka Upanishad 1.4.10)

अहम् ब्रह्मास्मि

“I am Brahman (God).”

Sanskrit: ayam atma brahma. (Brihadaranyaka Upanishad 4.4.5)

प्रज्ञानम् ब्रह्म

“Brahman is Consciousness.”

Sanskrit: prajnanam brahma. (Aitareya Upanishad 3.1.3)

सर्वं खल्व् इदं ब्रह्म

All this is Brahman.

Sanskrit: Sarvam khalvidam brahma. (Chandogya Upanishad 3.14.1)

Some Important Statements of Upanishads

Some illuminating verses of Paingal Upanishad

IV-12. When with the knowledge, ‘I am That !’ ‘I am That’ — I, whose mind is pure essence, is pure Spirit, is long-suffering – wisdom is won, when the object of knowledge, the supreme Self, is established in the heart; when the body is dissolved in the state of achieved Peace, then one becomes destitute of the luminous mind and intellect.

IV-13. Of what use is water to one who has had his fill of ambrosia ? Similarly, (for one) who has known his Self, of what use are the Vedas ? No duty remains for the Yogin who has had his fill of the ambrosia of knowledge. If duty be there, he is no knower of Truth. Though stationed at a distance, he is not distant; though embodied, he is disembodied; he is the omnipresent inner self.

IV-14. Making the heart pure, contemplating the well-being (of all), one must experience supreme joy in the thought, ‘I am the supreme, the All’.

IV-15. As there is non-difference when water is poured in water, milk in milk and ghee in ghee, so is the case with the individual Self and the supreme Self.

IV-16. When the body is burned by knowledge and knowledge becomes infinite in form, then the knower consumes the bondage of Karma in the fire of Brahman-Knowledge.

IV-17. Thence (follows the state of) the holy non-dual(Reality), named the Supreme Lord, like unto the stainless sky. Self’s nature, abiding without adjuncts, is as (that of) water mixed with water.

IV-18. Like the ether the Self in the subtle body. The inner Self like air is not perceived. That stirless inner Self perceives the external (manifold) with the torch of (objective) knowledge.

IV-19. The knower, dead, no matter due to whatever (form of) death, is dissolved (in Brahman that is) like the all-pervasive sky.

IV-20. This dissolution he knows in truth as of the pot-space (in the infinite space). He attains (the status of) the self-sustained light of all-pervasive knowledge.

IV-21. Standing on one foot, let man do austerities for a 1000 years; but (that austerity) is less than one sixteenth of this Yoga of meditation.

IV-22. This is knowledge; this is to be known; one wishes to know all that. Were he to live (even) for a 1000 years, he would not reach the end of the Shastras.

IV-23. What should be known is just the Imperishable; (but) life is fleeting. Avoiding the labyrinths of Shastras, meditate on the Truth (alone).

IV-24. Action are endless – purification, mutterings, (of holy names), sacrifices, pilgrimage to holy places. These (are valid) only till Truth is won.

IV-25. As regards the great-souled ones, the sure cause of liberation is (the knowledge) ‘I am Brahman’. The two words determining bondage and liberation are ‘mine’ and ‘not mine’.

IV-26. The import of ‘mine’ binds the living being; he is liberated by that of ‘not mine’. When the mind is dementalised, no longer is duality cognised.

IV-27. When dementalisation is achieved, That becomes the supreme status. Wherever, then, the mind goes, there, verily, is the supreme status.

IV-28. Thus, there, everywhere, is Brahman well-established. For one who holds ‘I am not Brahman’ no liberation is possible; (it is as futile) as striking the sky with clenched fists or a hungry man’s chewing the chaff.

IV-29. Whoso studies the Upanishad as a rule (every day) is purified by fire (as it were); by air; by the sun; by Vishnu; by Rudra. He has bathed in all sacred waters. He is versed in all the Vedas; has performed all the sacred rites taught by all the Vedas. He has ritually muttered Lacs of Itihasas and Puranas and one Lac times Rudra’s (tantras). He has muttered a million times the sacred syllable, OM. He redeems ten generations of his line, past and future. He purifies the rows of diners of which he is a number. He becomes great. He is purged of the sins of Brahmin-slaughter, drink, stealth, adultery with (even a) teacher’s spouse and of association with those who are guilty of these.

IV-30. That supreme Status of Vishnu spread out, like an eye, in the sky, the enlightened ones always behold.

IV-31. The wise, ever vigilant and diligent in praise richly glorify That supreme Status of Vishnu.

IV-32. OM-Truth – This is the secret teaching.

Om! That (Brahman) is infinite, and this (universe) is infinite.

The infinite proceeds from the infinite.

(Then) taking the infinitude of the infinite (universe),

It remains as the infinite (Brahman) alone.

Om! Let there be Peace in me!

Let there be Peace in my environment!

Let there be Peace in the forces that act on me!

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