The Aitareya Upanishad belongs to fourth, fifth and sixth chapters of the second book of AitareyaAranyaka of the Rigveda and considered as the oldest Upanishads. The Upanishad is divided into three chapters followed by thirty three verses.
The Aitareya Upanishad deals with philosophy of the Vedic religion, including soul, creation, birth and rebirth etc. ,the importance of food, manifestation of the Brahman and the ultimate path for salvation. It presents the ultimate spiritual truth “Who is he whom we meditate on as the Self? Which is the Self?
Everything are various names only of Knowledge (the true Self), Everything is led (produced) by knowledge.
It rests on Knowledge. The world is led by Knowledge. Knowledge is its cause. Knowledge is Brahman.” (AA, Chapter 3).
It describes Brahman as the Ultimate reality and emphasizes on mental purity and self-perfection.