The whole of the Vedantic essence in just one mantra

The heart of Vedanta ‘Brahma Satyam jagat mithya, jivo brahmaiva na aparah’ (Brahman alone is the transcendental Real and the apparent world is not real and the individual jiva is none other than Brahman)  is encapsulated in the mahavakya mantra of the Chandogya Upanishad:

स य एषोऽणिमैतदात्म्यमिदं सर्वं तत्सत्यं स आत्मा तत्त्वमसि श्वेतकेतो
Sage Uddalaka addresses his son Shvetaketu: The subtle Sat, Brahman, is the fundamental cause of this creation. This is the Atma. You are That.’This part of the above passage //The subtle Sat, Brahman, is the fundamental cause of this creation.This is the Atma//  teaches, based on another passage of this very Upanishad –  स य एषोऽणिमैतदात्म्यमिदं सर्वं तत्सत्यं स आत्मा which means ‘Have you known that one whose knowledge amounts to knowing everything?’ and replies giving the analogies of clay – clay products, gold – gold products and iron – iron products.  The transformations are mere names and insubstantial as names and forms but the substance in them is their material cause, clay, etc.

Based on this analogy, the mantra part स य एषोऽणिमैतदात्म्यमिदं सर्वं तत्सत्यं स आत्मा  (The subtle Sat, Brahman, is the fundamental cause of this creation. This is the Atma’) teaches: Brahman alone is real and the world is unreal. 
The other part of the mantra तत्त्वमसि श्वेतकेतो means ‘the jiva is none other than Brahman’
In this manner, the Chandogya Upanishad, one among the principal ten, teaches, just in one sentence, the seminal purport of the entire Vedanta.  
The statement ‘Brhama Satyam……….’ is established in the Niralambopanishat:
https://sanskritdocuments.org/doc_upanishhat/niralamba.html

Om Tat Sat