Ādi) Śaṅkarācārya works in Sanskrit discuss the unity of the ātman and Nirguna Brahman “brahman without attributes”.He wrote copious commentaries on the Vedic canon (Brahma Sutras, Principal Upanishads and Bhagavad Gita) in support of his thesis.His works elaborate on ideas found in the Upanishads. Shankara’s publications criticised the ritually-oriented Mīmāṃsā school of Hinduism. He also explained the key difference between Hinduism and Buddhism, 
stating that Hinduism asserts “Atman (Soul, Self) exists”, while Buddhism asserts that there is “no Soul, no Self”.
Ādi) Śaṅkarācārya travelled across the Indian subcontinent to propagate his philosophy through discourses and debates with other thinkers. He established the importance of monastic life as sanctioned in the Upanishads and Brahma Sutra, in a time when the Mīmāṃsā school established strict ritualism and ridiculed monasticism. He is reputed to have founded four mathas (“monasteries”), which helped in the historical development, revival and spread of Advaita Vedanta of which he is known as the greatest revivalist. Adi Shankara is believed to be the organiser of the Dashanami monastic order and unified the Shanmata tradition of worship. He is also known as Adi Shankaracharya, Shankara Bhagavatpada, sometimes spelled as Sankaracharya, (Ādi) Śaṅkarācārya, Śaṅkara Bhagavatpāda and Śaṅkara Bhagavatpādācārya.
The treasure I have found cannot be described in words, the mind cannot conceive of it.
Like the appearance of silver in mother of pearl, the world seems real until the Self, the underlying reality, is realized.
You never identify yourself with the shadows cast by your body, or with its reflection, or with the body you see in a dream or in your imagination. Therefore you should not identify yourself with this living body either.
What is enquiry into the Truth? It is the firm conviction that the Self is real, and all, other than That, is unreal.
But the jiva [living being] is endowed with ego and his knowledge is limited, whereas Ishwar is without ego and is omniscient.
