Krishna is the eighth avatar of Vishnu and is thought my most Hindus to be the supreme god. In the epic poem Bhagavad-Gita Arjuna, a Hindu prince, is in a great battle against his cousins over the throne. He is accompanied on the battlefield with his charioteer Krishna. As he scans the enemy's lines he notices several of his family and friends are standing there. He realizes that he will have to kill end up killing them to win the battle so he tells Krishna that he will not fight.
Krishna immediately tries to influence Arjuna to continue with the battle. He tells him that he would be viewed as a coward and that he needs to set a strong example for his people. Krishna also tells him he cannot deny his dharma as a warrior and member of the kshatriyas. He tells Arjuna not to fear for his family for they will reborn as the rules of samsara dictate.
Krishna then discusses moksha, the life goal of many Hindus, where he breaks away from samsara and is not reborn but rejoins Brahman or the very fiber of the universe. He then tells Arjuna how to achieve moksha. There is the way of knowledge, which is usually reserved for the Brahmins or priests; and there is the way of devotion which anyone may follow. The way of devotion involves being totally devoted to God and performing every act for that God without expectations of reward.
Even after all this persuading Arjuna is still not convinced so Krishnu finally reveals his true self to him which is the form of Vishnu the eternal Brahman. Arjuna responds that the revelation that his charioteer is actually the great god Vishnu is like the light of a thousand suns in the sky.