The Bhagavad-Gita is a standard book of knowledge coming down from time immemorial. As stated by Lord Sri Krishna Himself in the Gita, He first spoke the Bhagavad-Gita to the Sun-God Vivasvan. According to a rough estimate, this was at least 120,400,000 years ago! It was again shared by the Lord to Arjuna in the battlefield of Kurukshetra about five thousand years ago.
The Bhagavad-Gita, also called Gitopanishad, is the essence of Vedic knowledge. The study of the Vedas and Puranas – verily, the study of all scriptures can be said to have been completed in all respects by one who has studied the Bhagavad-Gita with devotion.
It is stated in the Gita-mahatmyam: One may cleanse himself daily by taking a bath in water, but if one takes a bath even once in the sacred Ganges water of the Bhagavad-Gita, for him the dirt of material life is altogether vanquished.