There are a number of forms of knowledge in the world. The West has especially focused on a process of observation of distinctions, organization, classification and an intellectual management of the implications of these distinctions. This has turned out to be a great power for action in the physical world. This type of knowledge, however, does not provide any depth of self-knowledge, nor does it provide insight to the wholeness and oneness of the universe. It is based on the use of mental faculties of logic, reason, deduction and relies on sense perceptions and memory as tools of this process. This type of knowledge is subject to constant correction as new facts become known and thus, it is a process of trial and error, an indirect process of knowledge.
The seers and sages of the Upanishads took a somewhat different approach, and looked for knowledge that was direct, immediate and incontrovertible. They wanted to determine, ‘that which, being known, all is known.’ They focused on developing the tools, internally, to experience knowledge by identity, a form of knowledge which would not be subject to change as new facts became evident, because it directly perceived and understood the truth of things. Such a process required them to take up practices that would remove the influences and limitations of the body, life-energy, and mind from their interference with that direct knowledge.
Sri Aurobindo observes: “It is because these seers saw Truth rather than merely thought it, clothed it indeed with a strong body of intuitive idea and disclosing image, but a body of ideal transparency through which we look into the illimitable, because they fathomed things in the light of self-existence and saw them with the eye of the Infinite, that their words remain always alive and immortal, of an inexhaustible significance, an inevitable authenticity, a satisfying finality that is at the same time an infinite commencement of truth, to which all our lines of investigation when they go through to their end arrive again and to which humanity constantly returns in its minds and its ages of greatest vision. The Upanishads are Vedanta, a book of knowledge in a higher degree even than the Vedas, but knowledge in the profounder Indian sense of the word, jnana. Not a grasping of a mental form of truth by the intellectual mind, but a seeing of it with the soul and a total living in it with the power of the inner being, a spiritual seizing by a kind of identification with the object of knowledge is jnana. And because it is only by an integral knowing of the self that this kind of direct knowledge can be made complete, it was the self that the Vedantic sages sought to know, to live in and to be one with it by identity. And through this endeavour they came easily to see that the self in us is one with the universal self of all things and that this self again is the same as God and Brahman, a transcendent Being or Existence, and they beheld, felt, lived in the inmost truth of all things in the universe and the inmost truth of man’s inner and outer existence by the light of this one and unifying vision.”
Sri Aurobindo, The Upanishads, Introduction, pp. 3-4