Summary: Aum, the sacred sound, is declared to be the ultimate reality and the means to realize the essence of Atman. The Mandukya Upanishad, with the Karika by Gaudapada, elucidates the non-dual nature of Atman through four chapters, beginning with the Agama Prakarana. By negating creation and delving into illusion, the text establishes the illusory nature of both dream and waking experiences, attributing them to the mind's creations. The significance of Aum as the support and essence of Brahman is emphasized, linking it to the non-dual Atman. Aum, representing the past, present, future, and beyond, is equated with the entire manifested world, revealing the interconnectedness of the material realm with the ultimate reality.