Chapter 13 - The Sphere Of Action And its Knower.The Thirteenth Chapter, in the Upanishad of the Shreemad Bhagwad Geeta, on the Knowledge of the Supreme Spirit, the Science of Yoga, is the Dialog between Krishna and Arjun, entitled : “Kshetr-Kshetragya Vibhag Yog’’ or ‘‘The Sphere of Action and its knower.’’