Lord Krishna said: I revealed this immortal yoga to Vivasvan (Sun-God), Vivasvan conveyed it to Manu (his son) and Manu imparted it to (his son) Iksvaku. But through long lapse of time, this yoga got lost to the world. The same ancient yoga which is the supreme secret has this day been imparted to you by me because you are my devotee and friend.
Arjuna said: You are of recent origin while the birth of Vivasvan dates back to remote antiquity. How then am I to believe that you imparted this yoga at the beginning of the creation?
Lord Krishna said: Arjuna, you and I have passed through many births. I remember them all but you do not remember. Though birthless, immortal and the lord of all beings, I manifest myself through my own yogamaya (divine potency) keeping my nature (Prakriti) under control. Arjuna, whenever righteousness is on the decline and unrighteousness is in the ascendant, then I body myself forth. My birth and activities are divine. He who knows this in reality is not reborn on leaving his body but comes to me.
In this world of human beings, men seeking the fruit of their activities worship the gods; for success born of actions follows quickly. He who has totally given up attachment to actions and their fruits no longer depends on anything in this world. He is ever content, does nothing at all though fully engaged in action. The Karmayogi who is contented with whatever is got unsought is free from jealousy and has transcended all pairs of opposites like joy and grief , success and failure, is not bound by his action.
Arjuna, when you have achieved enlightenment, ignorance will delude you no more. In the light of that knowledge, you will see the entire creation first within your own self and then in me. Even if you were the most sinful of all sinners, this knowledge alone would carry you like a raft across all your sins.
In this world there is no purifier as great as knowledge; he who has attained purity of heart through prolonged practice of Karmayoga automatically sees the light of truth in the self in course of time. Therefore Arjuna, slashing to pieces with the sword of knowledge this doubt in your heart born of ignorance and establish yourself in Karmayoga in the shape of even-mindedness and stand up for the fight.