Many people think that the concept of Non duality has been introduced by Adi Shankara as a new doctrine. But in reality, the facet of non duality / Advaita exists since the origin of this universe and the same has been documented in the Upanishads as the world itself is the direct creation of the non dual observer that is expressing through human forms.
However, during the time when Adi Shankara made a journey across distant lands, the knowledge was lost. So he re-established the concept of Advaita, the non duality and openly said that God is expressing a human and Jiva and Deva are one! Thus, he went on having various debates with scholars across the country and in the end they’re all left awestruck with this startling knowledge uttered by the ancients which then reaffirmed by Adi Shankara.
The term non duality itself states ‘oneness’ and one might ask that if it can be said as such, why say the word non duality? Then the answers is, the human is blinded by forgetfulness and his ignorance, he only believes what his senses say, which are nothing but the electrical signals interpreted by the brain. So, to him, it appears that God is different from him, that he stays somewhere else. So, the Upanishads, and Adi Shankara said that, instead of ‘One’ it ‘Non’Duality’ to make it easy for humanity to understand their divinity.
Viswanath Venkat Dasari