The Bhagavad Gita is one of the most important texts of Hinduism, documenting the discussion between Prince Arjuna and his guide and charioteer Lord Krishna as they prepare for battle to fight a righteous war between Pandavas and Kauravas. The text, commonly referred to as the Gita, was written in Sanskrit sometime between 1000 B.C. and 700 B.C.
The Bhagavad Gita is recounted through the eyes of Sanjaya, a wise old sage who tells the story to the blind King Dhritarashtra. Prince Arunja first tells Lord Krishna that he does not want to fight and shed blood for a kingdom when he doesn't even know if he wants the kingdom. Krishna then explains why it is Arunja's dharmic duty to fight him, and he explains how he must do it in order to restore his karma.
Throughout their discussion, Krishna synthesizes various concepts of Hinduism. He presents the samsaric cycle of birth and death, explaining that there is no death of soul and that one simply sheds his temporary body at the end of each cycle. Krishna explains that the purpose of this cycle is to allow individuals to work their karma with each new body, with the goal of achieving the a dissolution of the soul and achieving enlightenment.
Krishna presents the three main concepts needed to achieve this final state of the soul, which are renunciation, selfless service and meditation. These are the three elements of yoga, the mental and physical practice of achieving divine action.
In the end of the Bhagavad Gita, Krishna explains that Arunja must choose between the paths of good and evil and that he can correct the balance of good and evil by fighting the righteous war.