Chandogya Upanishad is one of the oldest Upanishads written on the Vedic Brahmana period about ninth to eighth century B.C. Chandogya Upanishad is associated with Sama Veda. It is the part of Chandogya Brahaman that contains ten chapters. The 14th Khanda of Chapter Three of Chandogya Upanishad states about the Sandilya Doctrine. According to this everything is Brahman. The universe has evolved from the Brahman and then merges in it. The universe breathes in it and also all the beings lives in it. Thus, all beings must adorn it and also meditate on Brahman with a calm mind and try to attain it. A man consists of will. He becomes what he wills to be when he has departed. A man must be allowed to form his will with the knowledge. This knowledge must be associated with the real Self.
The khanda also explains about the real Self. It is the one that consists of the mind, whose form is light, whose thoughts are true, whose nature is like the akasa, whose body is subtle, who treasures righteous desires, who has created the universe. The Self is also the one who has, who has all the tastes of the world, who embraces everyone, does not speaks and exists with any desires and longings. The Self resides within the heart of all in a form that is smaller than a grain of rice, smaller than a mustard seed, smaller than a grain of barley, smaller than a grain of millet. The Self is greater than everything. It is greater than the earth, greater than the mid region, greater than heaven, greater than all the worlds. The Self is further explained as the one who has created the universe and all the beings, who cherishes all desires, who contains all odours, who is endowed with all tastes, who embraces all this. One who knows this and realises that the Self resides in the heart and the creator of everything, understands that he is the Supreme Brahman. All beings after departing from this world unite with Him. One who has this faith and has no doubt will certainly attain to that Godhead.
