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 witness of the three states of consciousness [waking, dream and deep sleep] and of the nature of Existence-Consciousness-Bliss is the Self.
All the manifested world of things and beings are projected by imagination upon the substratum which is the Eternal All pervading Vishnu , whose nature is Existence- Intelligence ; just as the different ornaments are all made out of the same gold.
Thus one should know oneself to be of the nature of Existence-Consciousness-Bliss[Sat-Chit-Ananda].
Space seems broken and diverse because of the many forms in it. Remove the forms and pure space remains. So, too with the Omnipresent Self.
Who but the Atman is capable of removing the bonds of ignorance, passion and self-interested action?