In Chapter four, Shree Krishna strengthens Arjun’s faith in the knowledge he is imparting to him by revealing its pristine origin.Lord Krishna explains  how this is an eternal science that he taught in the beginning to the Sun God, and it was passed on in a continuous tradition to saintly kings. He is now revealing the same supreme science of Yoga to Arjun, who is a dear friend and devotee.

Arjun is quite surprised and  asks how Shree Krishna, who exists in the present, could have taught this science eons ago to the Sun God. In response, Shree Krishna discloses the divine mystery of his dissension. He explains that though God is unborn and eternal

However, his birth and activities are both divine, and never tainted by material imperfections. Those who know this secret engage in his devotion with great faith, and on attaining him, do not take birth in this world again.

The chapter then explains the nature of work, and discusses three principles—action, inaction, and forbidden action. It discloses how karm yogis are in the state of inaction even while performing the most engaging works, and thus, they are not entangled in karmic reactions. With this wisdom, the ancient sages performed their works, without being affected by success and failure, happiness and distress, merely as an act of sacrifice for the pleasure of God. Sacrifice is of various kinds, and many of them are mentioned here. When sacrifice is properly dedicated, its remnants become like nectar. By partaking of such nectar, performers are cleansed of impurities. Hence, sacrifice must always be performed with proper sentiments and knowledge. With the help of the boat of knowledge, even the biggest sinners can cross over the ocean of material miseries. Such knowledge must be learnt from a genuine spiritual master who has realized the Truth. Shree Krishna, as Arjun’s Guru, asks him to pick up the sword of knowledge, and cutting asunder the doubts that have arisen in his heart, stand up and perform his duty.

therefore, with the sword of knowledge, cut asunder the doubts that have arisen in your heart. O scion of Bharat, establish yourself in karm yog. Arise, stand up, and take action