Srila Prabhupada gave regular Bhagavad-gita classes and we have video recordings of a few and audio recordings of hundreds of Bhagavad-gita classes. Bhagavad-gita contains the essence of all spiritual knowledge. It is a conversation between Krishna, the Supreme Personality of Godhead and His friend Arjuna. This conversation took place just before the greatest battle that has ever taken place on this planet. It was at a place called Kuruksettra in India. Arjuna did not want to fight but Krishna was encouraging Arjuna to fight. Ultimately Arjuna surrendered to Krishna and fought in the battle and was victorious but with practically all the fighters on both sides killed.