In Kashi, Shankara propounded the philosophy of Advaita, which holds that there is one substratum of Reality behind the entire universe. What appears externally as dual, or many, is unreal. It is the Self within which reflects one Reality, Brahmn. The individual functions in connection with the mind, body and senses, which limits his supreme divine nature and obscures his vision. Realising one is not the body, mind or intellect and consciousness of the Self leads to spiritual fulfilment.
Though Sankara was an embodiment of Jnana, the eternal wisdom, he also emphasised the importance of devotion. According to him, when the devotion matures, it leads to Jnana.
Shankaracharya Jayanti falls on May 12