Upanishads are solid chunks of direct esoteric knowledge.
Straight from the Seer's mouth. No mediators! The most powerful Yogis of ancient India put down their feelings, hints and realizations about the Infinite Omnipresent
Impersonal God in the Upanishads. You may consider Upanishads as the essence of all Vedic knowledge. There are 4 Vedas. The principal Upanishads are derived from the 4 vedas. Later Gists of Knowledge about various disciplines of philosophy such as Yoga, came to known as Upanishads. Like the Yoga-Sara-Upanishad, etc. But they are considered lesser to the eleven I have mentioned above.
Brihadaranyaka-Upanishad is the most significant and perhaps one of the Largest of the Upanishads. Brihath= Large, Aranyaka= Forest life (of the Yogis).
Upanishad, the word needs clarification.
Upa + ni +sad.
Upa= nearness, or reaching somewhere or knowing about something.
Ni= with clarity, uncloudedness, certainty;
sad or
sath= Truth, Unwavering, Unshakable, Everlasting. Sat is a
root word synonymous to Om or Tath or
That meaning God impersonal.
If we add them up,
Upanishad means
Clearly Knowing God.
Later on, Upanishads came to be regarded as the basis of pure Lore, collectively called the
Vedanta philosophy.
Veda =To know, Anta= end. The end of Veda= the essence of Veda. It primarily includes Upanishads & Gita.
Indian Knowledge
Yogishwara ==> Veda (undifferentiated) ==> Upanishads ==> 4 Vedas ==> Ramayana, Mahabharata epics ==> 18 Puranas ( Bhagavat Purana = imp) ==> Tantras
Yogishwara = Yoga Adepts of unimaginable capacity
Yoga + Ishwara. Ishwara= supreme master or god.