The influence of the Upanishads world-wide has been pervasive and enormous. Numerous religions that have arisen in India rely heavily on the Upanishadic view, not the least of which is the Vedanta. The Upanishads have also found their way to the West and have been translated numerous times by Western scholars. The West, fixated upon the physical world, however, has tended to try to translate the body, the words and expressions of the Upanishads without necessarily getting at the spirit or substance that enlivens them and makes them the source of inspiration. It is difficult for a modern researcher to appreciate the rich inner life of the seers of the Upanishads when the time-spirit is so different. Yet any pertinent review of the Upanishads must necessarily get at the spirit and bring it forth.
Sri Aurobindo observes: “This character of the Upanishads needs to be insisted upon with a strong emphasis, because it is ignored by foreign translators who seek to bring out the intellectual sense without feel the life of thought-vision and the ecstasy of spiritual experience which made the ancient verses appear then and still make them to those who can enter into the element in which these utterances move, a revelation not to the intellect alone, but to the soul and the whole being, make of them in the old expressive word not intellectual thought and phrase, but sruti, spiritual audience, an inspired Scripture.”
“The Upanishads have been the acknowledged source of numerous profound philosophies and religions that flowed from it in India like her great rivers from their Himalayan cradle fertilising the mind and life of the people and kept its soul alive through the long procession of the centuries, constantly returned to for light, never failing to give fresh illumination, a fountain of inexhaustible life-giving waters.”
Much of Buddhist philosophy derives from Upanishadic thought. “The ideas of the Upanishads can be rediscovered in much of the thought of Pythagoras and Plato and form the profoundest part of Neo-Platonism and Gnosticism with all their considerable consequences to the philosophical thinking of the West…. The larger part of German metaphysics is litter more in substance than an intellectual development of great realities more spiritually seen in this ancient teaching, and modern thought is rapidly absorbing them with a closer, more living and intense receptiveness which promises a revolution both in philosophical and religious thinking; here they are filtering in through many indirect influences, there slowly pouring through direct and open channels. There is hardly a main philosophical idea which cannot find an authority or a seed or indication in these antique writings…. And even the larger generalisations of Science are constantly found to apply to the truth of physical Nature formulas already discovered by the Indian sages in their original, their largest meaning in the deeper truth of the spirit.”
Sri Aurobindo, The Upanishads, Introduction, pp. 2-3