Why Krishna Came to the Mahabharat

The Gita gives the answer in its fourth chapter, in the verses beginning yada yada hi dharmasya: whenever right conduct declines and its opposite rises, he takes form again. It is the epic's own explanation of his presence, stated by him, and it is the passage most often quoted from the whole work.

What is striking is how little he does with that authority. He carries no weapon into the war, drives a chariot, negotiates, and argues. The intervention the verses promise turns out to consist almost entirely of talking to one man at the worst moment of his life.