The Message of the Upanishads is a study, verse by verse, of three of the principal Upanishads, namely, Isa, Kena, and Katha. The first contains eighteen, the second thirty-five, and the third one hundred and nineteen verses. Though constituting a small portion of the total Upanishadic literature, they yet contain a lucid exposition of all the essential ideas of this immortal literature.

Scholars are divided as to the date of the composition of the Upanishads. Many of them are agreed, however, that most of the principal Upanishads belong to the period prior to the event of Buddha in the seventh century before Christ. There are over two hundred Upanishads, many of them sectarian in character and palpably post-Buddhistic and even post-Sankaracharya.

The principal Upanishads are accepted to be those which Sankaracharya (A.D. 788-820) chose to comment upon; they are ten in number and are enumerated in the Indian tradition as follows:, Isa, Kena, Katha, Prasna, Mundaka, taittiriya, Aitareya, Chandogya, and Brhadaranyaka.

According to some scholars, Sankara also commented on an eleventh Upanishad, the Svetasvatara. In his commentary on the Brahma-Sutra, he refers to four more, namely, Kausitaki, Jabala, Mahanarayana, and Paingala.

The Isa Upanishad embodies in its very opening verse the central theme of all the Upanishads, namely, the spiritual unity and solidarity of all existence.

The Kena illumines the nature of knowledge by pointing out the eternal known behind all acts of knowing, and purifies man's concept of ultimate reality of all touch of finitude and relativity by revealing its character as the eternal Self of man and the Self of the universe.

The Katha holds a special fascination for all students of the Upanishads for its happy blend of charming poetry, deep mysticism, and profound philosophy; it contains a more unified exposition of Vedanta than any other single Upanishad; its charm is heightened by the two characters of its dialogue, namely, old Yama, the teacher, and young Naciketa, the student.

The Prasna, as its name implies, is an Upanishad of questions; each of its six chapters comprises a question asked by each of a group of six inquiring students on various aspects of Vedanta, and the answers given by their teacher, the sage Pippalada.

The Mundaka, after classifying all knowledge into para, higher, and apara, lower, and describing all science, art, literature, politics, and economics – in fact, all positive knowledge, the knowledge of the changeful many – as apara, and boldly including even the holy Vedas and all sacred books in this category, proclaims that one knowledge as para 'by which the imperishable changeless reality (of the One behind the many) is realized'. And the Upanishad sings in ecstasy the glorious vision of the One in the many.

In the brief compass of its twelve verses of condensed thought, the Mandukya surveys the whole of experience through a study of the three states of waking, dream, and dreamless sleep, and reveals the Atman, the true Self of man, the Turiya or the Fourth, as it puts it, as pure consciousness, eternal and non-dual. It a pregnant utterance – one of the four mahavakyas or 'great utterances' of the Upanishads; ayam atma brahma – 'This Atma (Self of man) is Brahman.'

The Taittiriya, after majestically proclaiming that 'the knower of Brahman attains the Supreme': Brahmavidapnoti param, describes the five kosas or sheaths that enclose and hide Brahman, and demonstrates the technique of piercing these sheaths of relativity and finitude with a view to reaching the infinite and the eternal at the core of experience. It also provides a scientific definition of Brahman as 'That from which all these beings are born, by which, after being born, they live, and into which they merge when they cease to be'.

The Aitareya establishes the spiritual character of the Absolute through a discussion of the nature of the Self of man, and proclaims this truth in another of the four mahavakyas (V.3): Prajnanam brahma – 'Brahman is pure Consciousness.'

The Chandogya introduces us to charming truth-seekers like Satyakama, Svetaketu, and Narada, and outstanding spiritual teachers like Aruni, Sanatkumara, and Prajapati. Through several illuminating teacher-student dialogues, the Upanishad helps us to discriminate the utterance of deep spiritual and philosophical import, treated as another of the four mahavakyas, it sings in refrain the divinity of man: tat tvam asi – 'That thou art.' It prescribes knowledge of this innate divinity of man as the one remedy for the deeper ills of life (VI.8.7): tarati sokam atmavit – 'The knower to the Atman crosses all sorrow.' In its profoundly human episode of the discipleship of India under Prajapati, it instructs us in the true nature and technique of man's spiritual quest and the blessings that flow from spirituality. It is an impressive account of man's spiritual education, his growth from worldliness to spirituality. It points out the limitations of materialism as a philosophy of life and the evils that flow from it.

The Brhadaranyaka, the longest of the Upanishads, is, as its name implies, a big (brhat) forest (aranya) of philosophical thought and spiritual inspiration. Four outstanding personalities illumine its pages – two men and two women – Janaka, the philosopher-king, Yajnavalkya, the philosopher-sage, Maitreye, the deeply spiritual wife of Yajnavalkya, and Gargi, the vacaknavi, the 'gifted women speaker and philosopher', who is foremost among the questioners of Yajnavalkya in philosophical debate. The Upanishad majestically expounds, through its fascinating dialogues conducted by these outstanding and other lesser personalities, the central theme of all the Upanishads, namely, the divinity of man and the spiritual solidarity of the whole universe in Brahman. It contains another of the four mahavakyas (I.4.10), namely, aham brahmasmi – 'I am Brahman', besides the ayam atma brahma of the Mandukya already referred to. It dares to characterize Brahman as 'the fearless', and presents its realization by man as the attainment, here and now, of the state of absolute fearlessness and fullness of delight.

It goes to the eternal credit of Sankara that, through his masterly commentaries on the principal Upanishads, he brought out of obscurity this immortal literature, as also the great Bhagavad-Gita, and made them accessible and intelligible to a wider audience; and that audience has been steadily widening ever since, aided by the contributions of subsequent commentators, thinkers, and sages, until, in the present age, thanks to the techniques of modern western civilization, the whole world has become its actual or potential audience. Apart from the great western orientalists, whose translations and expositions brought this and other books of the Indian tradition to the attention of scholars in East and West, it was from Swami Vivekananda, the most authentic voice of Vedanta in the modern age, that vast masses of men and women in both the hemispheres became drawn to the spiritual charm and rational strength of this literature and to a recognition of its relevance to man in the modern age. In his lecture on 'Vedanta and Its Application to Indian Life', the Swami says (Complete Works, Vol. III, Eighth Edition, pp. 237-38):

'Strength, strength is what the Upanishads speak to me from every page. This is the one great thing to remember, it has been the one great lesson I have been taught in my life. Strength, it says, strength, O man, be not weak. Are there no human weaknesses? – Says man. There are, say the Upanishads, but will more weakness heal them, would you try to wash dirt with dirt? Will sin cure sin, weakness cure weakness… Ay, it is the only literature in the world where you find the word abhih 'fearless', used again and again; in no other scripture in the world is this adjective applied either to God or to man…. And the Upanishads are the great mine of strength. Therein lies strength enough to invigorate the whole world. The whole world can be vivified, made strong, energized through them. They will call with trumpet voice upon the weak, the miserable, and the down-trodden of all races, all creeds, all sects, to stand on their feet and be free. Freedom – physical freedom, mental freedom, and spiritual freedom – are the watch-words of the Upanishads.'

Samara's commentaries of these Upanishads, especially on those of their passages pregnant with philosophical and spiritual import, are masterpieces of philosophical discussion illumined by deep spiritual insights. His masterly handling of the Sanskrit language in these commentaries gives us a prose which is marked by brevity and vigour, simplicity and poetic charm.

In the Upanishads, we get an intelligible body of verified and verifiable spiritual insights mixed with a mass of myths and legends and cosmological speculations relating to the nature and origin of the universe. While the former has universal validity, and a claim on human intelligence in all ages, the latter forswears all such claim. All positivistic knowledge contained in any literature, including religious literature, is limited and conditioned by the level of contemporary scientific knowledge. Modification, and even scrapping, of much of this knowledge due to subsequent advances has affected the truth-validity of much of man's literary heritage, including his religious and philosophical ones.

The spiritual insights of the Upanishads, however, are an exception to this tyranny of time. Subsequent scientific advances have not only not affected their truth-value but have, on the contrary, only helped to reveal the rational basis of their insights and enhance their spiritual appeal. This is no wonder, because these insights are the products of an equally scientific investigation into a different field of experience, namely, the world of man's inner life.

Born in the village of Trikkur, Kerala State, on December 15, 1908, Swami Ranganathananda joined the Ramakrishna Order, the international spiritual and cultural movement founded by Swami Vivekananda, at its branch in Mysore in 1926. he was formally initiated into Sannyasa in 1933 by Swami Shivananda, one of the eminent disciples of Sri Ramakrishna and the second president of the Order. After spending the first twelve years in the Order's branches in Mysore and Bangalore, the first six years of which as cook, dish-washer and house-keeper and later as warden of student's hostel, he worked as Secretary and liberation at the Ramakrishna Mission branch at Rangoon – from 1939 to 1942, and thereafter as President of the Ramakrishna Math and Mission, Karachi, from 1942 to 1948.

From 1949 to 1962, he worked as the Secretary of the New Delhi branch of the Mission, and from 1963 to 1967, he was the Secretary of the Ramakrishna Mission Institute of Culture, Calcutta (Kolkatta), Director of its school of Humanistic and Cultural Studies, and Editor of its monthly journal.

From 1973 to 1993 he was President of Ramakrishna Math, Hyderabad. From 1994 to 1998 he was Vice-President of World-Wide Ramakrishna Math and Ramakrishna Mission and became its President in 1998. He stayed at Belur Math, till his passing away on April 25, 2005.

He was undertaken extensive lecture tours from 1946 to 1972 covering 50 countries. From 1973 to 1986 he visited annually Australia, U.S.A., Holland and Germany.

In 1986 he was awarded the first Indira Gandhi Award for National Integration.