Brhadaranyaka Upanishad is the ancient and elementary part of Upanishad. It is related to the Shukla Yajur Veda. The Brhdaranyaka Upanishad is the secondary extraction of the Brahamana text. It is a commentary on Purush Sukta of the Vedas and contains symbolism, metaphors and imagery for relating the nature of reality. The third chapter of part two of Brhadaranyaka Upanishad states about the forms of Brahman which are mortal and immortal, gross and subtle, definite and indefinite and limited and unlimited. The gross form is different from akasa and air. The essence of that which is gross, mortal, limited and definite is the sun that shines for it is the essence of that exists.

Anything that does not have any form is the air and the ether. This is immortal, infinite, and indefinite. The essence of that has no form, that which is immortal, infinite and beyond is the spirit present in this universe. This refers to the divine relation. Here it states the relationship of soul with air and akasa. Whatever is immortal is unlimited and indefinite. That which is subtle, immortal, unlimited and which is indefinite is the person or Purusha in the solar orb. That person becomes the essence of the two elements that exists. This has been stated with reference to the gods. With reference to the subtle, it is the air and the akasa that is in the body. It is immortal, unlimited and is indefinite. The essence of that which is subtle, which is immortal, which is unlimited and which is indefinite is the Purusha that is in the right eye. The form of this spirit appears like a cloth dyed in turmeric, as the smoke colour of sheep wool, as the red colour of the Indragopa insect, as the bright colour of the fire flame, as the white colour of the lotus, as the lightning shines at one moment. He, who is aware of this, shines like a flash of lightning. Therefore the Brahman can be described as `the truth of truths.` The vital breath is truth and Brahman is the truth of that.