What is its specific Theme? What is The End In view? For Whom Is Its Teachings Intended?

 - What is its relation to other parts of the Veda? - The Specific Theme Of The Upanishad - The theme of a particular science ought to be that which is not treated of in any other scinece

- Drugs of various sorts, planetary motion, and right formation of words are said to be themes of Medicine, Astronomy, Grammar, respectively, because they are not treated elsewhere

- So the theme of this science of the Upanishad is Advaita, non-duality of the Self, which is not treated elsewhere.

- In fact, the non-duality of the Self is known from the Upanishad alone and from no other source of knowledge 

- And elsewhere in the ritualistic section, the Sruti says "He that knows not the Veda never thinks of Him, the Great" (Taittiriya-Brahmana 3-12-9)

- Just as this passage excludes all sources of knowledge other than the Veda, so another passage excludes all other parts of Veda except the Upanishad. 

- Accordingly the Vajasaneyins read "I ask of thee about Him, the Purusha of the Upanishads;" (Brihadaranyaka Upanishad 3-9-26) i.e., of Him who is treated of only in the Upanishad

- If there be any other source of knowledge concerning the Self, it must be wither pratyaksha (immediate perception), or anumana (empirical inference), agama (revelation).

- Pratyaksha again is of two kinds, the external or objective, and manasic or subjective. As to the first, the Talavakaras exclude it in the following words: "There sight goes not" (Kena Upanishad 1-3)