The sermon given by Lord Krishna to Arjun before the start of the Mahabharata war is called Srimad Bhagavad Gita. It is a part of Bhishma Parva in Mahabharata. Geeta has 18 chapters and 700 verses. The knowledge of Geeta was spoken about 5168 years ago (3145 BC) from today (2023). Geeta is counted in Prasthanatrayi, which also includes Upanishads and Brahmasutras. Therefore, according to Indian tradition, the place of Geeta is the same as that of Upanishads and Dharmasutras.
During the war of Mahabharata, when Arjun refuses to fight, Shri Krishna preaches to him and makes him aware of the true knowledge of karma and dharma. These teachings of Shri Krishna have been compiled in a book called “Bhagwat Geeta”.