Tatpurusha - That personified
The entire purport of the Vedas is contained in the four Mahavakyas, one of which is tattvamasi "you are that". What is the "that" which is being refered to? "That" is Brahman. What are the implications of knowing you are one with Brahman? In the chandogyopanishad it is related that Indra the Deva raja, and Virochana, the Asura raja both heard the Vedantic teaching. Virochan instantly thought "Oh, I'm God so I can do whatever I like." Indra on the other hand, grasped the real meaning that the equation of jiva and Brahman is meant to lessen the ego not give it free license. Thus for a while the Asuras prospered but in the end the Devas prevailed.
The snare of the ego or ahamkara is a strong and insidious one and even the mightiest find it difficult to resist. Once Shankaracharya was in Kashi and he awoke one morning to take his snana in the Ganga. As he approached the ghata his way was barred by a dom, one of the untouchable caste whose job is to cremate the dead in that city. Angrily, he ordered him out of the way. whereupon the dom replied, "How can a person who claims to shun the false world of names and forms talk about 'you' or 'me'?" Whereupon Shankaracharya instantly realized this was none other than Shiva Bhagawan come to teach him a lesson. Soon after the incident of the candaala in kaashi, shankara composed the stotra called maniishhaa pancakam. (five stanza-s)
Om tatpurushaya namah