The story of Uddalaka and his son Svetaketu is found in the Chandogya Upanishad. As per the tradition of the family in those days when the child turned twelve, the child was advised by his father to gather knowledge. Accordingly, Svetaketu had his education with a forest sage and returned home. On his return, Uddalaka noticed that his son Svetaketu carried a sense of pride on his face. The former realized that Svetaketu indeed had not realized the true knowledge of Brahman. So father Uddalaka teaches his son Svetaketu.
So, Uddalaka said, “Can you hear that which cannot be heard by the ear? Can you see what cannot be seen by the eyes? Can you know what cannot be known by the mind?”
Svetaketu was stunned at this and requested his father to teach him more.
At this, Uddalaka continued, “When you know one lump of clay, you know all that is made of clay. When you know one pair of iron tongs, you know all that is made of iron. When you know one nugget of gold, you know all that is made of gold.”
Without resting, Uddalaka said, “In the beginning, there was an unbounded ocean of Consciousness, one without a second (Ekam evadvitiyam). The ocean of Consciousness said, “I am one, may I be many.”
The light was created. Light thought to itself, “I am one, may I be many.”
Water was created. Water thought to itself, “I am one, may I be many.”
Thus the matter was created. The One became light, water, and matter, and the three became many. Thus the universe came into existence. But the essence of all creation is Self, the ocean of Pure Consciousness, that is Truth. That thou art (Tat tvam asi). When this is realized then one can see the unseen and know the unknown. One has known that by knowing which everything else becomes known. This is the true teaching of the Veda. Thus Svetaketu was enlightened.