The main acharya (teacher, preceptor) of Advaita Vedanta, Shankaracharya (788-820 A.D.) was a great Hindu mystic and scholar who brought about the greatest revival of Advaita Vedanta in Indian philosophy and spirituality. Adi Shankaracharya’s (adi means “first”) contributions to advaita thought and Hinduism in general are crucial. In his short lifespan, he alone was responsible for a country that was almost entirely Buddhist again becoming almost entirely Hindu. He revived monism in India and brought a profound understanding of existence. He wrote many commentaries on the sutras and shastras (the Upanishads, etc.) and gained many disciples through his power of spiritual debate. His most important lesson was that reason and abstract philosophizing alone would not lead to moksha (liberation). He believed that it was only through selflessness and love governed by viveka (discrimination) that a devotee could realize his inner Self.