The pinnacle of the wisdom and practices of the ancient sages is contained in the terse twelve verses of the Mandukya Upanishad, which outlines the philosophy and practices of the OM mantra (written as either AUM or OM). The three stages plus the fourth of Om mantra are central to Yoga Meditation, Advaita Vedanta, and Samaya Sri Vidya Tantra.
From:
http://www.swamij.com/om.htm
Duration : 0:9:29
http://www.swamij.com Nondualism is central to Advaita Vedanta and Yoga Meditation. Seek to know that by which knowing, The nature of all things is known, Seek to love that by which loving, That love beyond all forms is known. That by which knowing, loving, holding Comes Absolute Joy, The One Joy that is unbounded, unconditioned, Limitless.