The Bhagavadgita is a part of the Mahabharata epic. The purpose of this epic is to spread esoteric knowledge to the public—a knowledge which is difficult to get. The Mahabharata is a Smriti, which implies an easy rendering of a complex and esoteric text. Smriti is a text which is written, and not revealed, like the Shruti is. The Vedas are a revealed text and not written by any author.
As mentioned in one of the Gita Mahatmya verses, the Bhagavadgita is the essence of the Upanishads. Why was it necessary to give the essence? Because Kaliyuga was about to dawn, and truths which could be understood before now needed elaborate explanations, as people’s minds had become unfit to understand the subtleties of the Shrutis. Hence, it is profitable to behold the esoteric and mystical meaning of the Bhagavadgita. A truth not to be given to the masses, but only to initiated disciples. It is not that knowledge is to be hidden, but it should be avoided being given into wrong hands.
There is a scripture similar to the Bhagavadgita in many respects, called the Katha Upanishad, the one from which the Bhagavadgita-teachings are believed by many to have been drawn. If the Bhagavadgita is a conversation between Sri Krishna and Arjuna, placed in the context of the historical event of the Mahabharata war, the Katha Upanishad is a conversation between Yama and Nachiketas. Just as we have the confusion of Arjuna’s mind in the beginning of the Bhagavadgita, we find intense aspiration on the part of Nachiketas in the beginning of the Kathopanishad. There are four important stages in its teaching, even as the eighteen chapters of the Bhagavadgita reveal the stages of the sadhaka’s evolution.
The Katha is magnificient in its poetic beauty and mystical value. It touches the vital points of spirituality without beating about the bush. The verses or mantras are statements of human consciousness in its higher reaches of the spirit. This Upanishad takes an anecdote for its background. It occurs in the Taittiriya Brahmana portion of the Vedas which precedes the Kathopanishad:
Vajasravasa Gautama performed a sacrifice called Sarvavedas or Sarvadakshina, a sacrifice in which one is supposed to offer everything he has, without exception; hence its name Sarvadakshina. It is a preparation for the last stage of spiritual life. However, he was not really ready for it. He wanted to offer only things which were not useful, thus following the letter of law, but losing the spirit behind it. He had a young son, Nachiketas by name, who clearly saw the two defects in the sacrifice: the giving of weak and barren cows, and the father’s ignorance of the fact that the son, too, was to be offered. “Joyless,” said the boy, “are the regions to which he goes who offers such sacrifices!” thus irritating his father. And he asked him: “To whom are you going to offer me?” He repeated this question thrice, and the displeased Gautama answered angrily: “To death I send you!”
Here ends the outline of the story, and now we have the real beginning of the Upanishad—a direct teaching to the spiritual aspirant.
The Vedas contain four sections: the mantra portion called the Samhitas; the ritualistic portion called the Brahmanas (external sacrifice to the chanting of the Samhitas); the internal ways of sacrifice, the Aranyakas—which can also be called internal Brahmanas—which are sacrifices without involving materials; and the end-portion of the Vedas, the Upanishads, also known as Vedanta.