The chief reason why the Upanishads are called the end of the Veda is that they represent the central aim and meaning of the teaching of the Vedas. The content of the Upanishads is “Vedanta vijnanam”, the wisdom of the Vedanta. The Samhitas and the Brahmanas, which are the hymn and the liturgical books, represent the “karma-kanda” or the ritual portion, while the Upanishads represent the “Jnana-kanda” or the knowledge portion. The learning of the hymns and the performance of the rites are a preparation for true enlightenment.
The Upanishads describe to us the life of spirit, the same yesterday, today and forever. But our apprehensions of the life of spirit, the symbols by which we express it, change with time. All systems of orthodox Indian thought accept the authoritativeness of the Vedas, But give themselves freedom in their interpretation. This variety of Interpretation is made possible by the fact that the Upanisads are not the thoughts of a single philosopher or a school of philosophers who follow a single tradition.
They are the teachings of thinkers who were interested in different aspects of the philosophical problem and therefore offer solutions of problems which vary in their interest and emphasis. There is thus a certain amount of fluidity in their thought, which has been utilized for the development of different philosophical systems. Out of wealth of suggestions and speculations contained in them, different thinkers choose elements for the construction of their own systems, not infrequently even through a straining of the texts.
Though the Upanishads do not work out a logically coherent system of metaphysics, they give us a few fundamental doctrines which stand out as the essential teaching of the early Upanishads. These are recapitulated in the Brahma Sutra.
The Brahma Sutra is an aphoristic summary of the teaching of the Upanishads and the great teachers of the Vedanta develop their distinctive views though their commentaries on this work. By Interpreting the sutras which are laconic in form and hardly intelligible without interpretation, the teachers justify their views to the reasoning intelligence.