To strengthen Arjun's faith in the knowledge He is imparting, Shree Krishna reveals its pristine origin in this chapter. He says, "Arjun, as you are my devotee and a dear friend, I am revealing this supreme science of yog to you. It is the same eternal science that I taught to the Sun God at the beginning of time. And in a continuous tradition, the same knowledge; was passed to the saintly kings." Arjun wonders how someone who is almost his age could exist so many eons ago. He asks Shree Krishna how is it possible that you gave this knowledge to the Sun God and the others so many years back in time.
Shree Krishna clarifies Arjun's doubts and discloses the divine mystery of His descension. He says that although God is unborn and eternal, it is to establish dharma (the path of righteousness) that He descends on this earth by His Yogmaya power. His birth and activities are divine and cannot get tainted by material imperfections. Once a devotee knows this secret and engages in devotion with great faith, he attains God and does not take birth in this world again.
Then Shree Krishna goes back to karm yog, the subject from the previous chapter. He continues to explain the nature of work and its three principles: action, in-action, and forbidden action. He elaborates that the karm yogis, even while performing the most engaging task, are in the state of inaction and do not get entangled in the karmic reactions of such action. Knowing this: the ancient sages performed all their work as an act of sacrifice for the pleasure of God. They were not affected by happiness, distress, success, or failure. He explains that when sacrifice is suitably dedicated, performed with proper knowledge and pure sentiments, then its remnants become like nectar. And by partaking such nectar, the devotees are cleansed of all impurities. Even the biggest sinner can cross over the ocean of material miseries by boarding this boat of eternal knowledge.
Shree Krishna says that such knowledge should be acquired only from a genuine spiritual master, who himself is God-realized. Being his Guru, Shree Krishna instructs Arjun to cut apart all doubts that have arisen in his heart with this sword of knowledge. He asks Arjun to now get up and perform his duty as a warrior.