Krishna which is really an incarnation of Vishnu, the “Preserver God”, teaches Arjuna several things in their conversation. Arjuna is told to go fight in the Kurukshetra War. He is confused and had moral issues with doing this because he has relatives on the opposing side. He also doesn’t understand or want to kill because he thinks it would be bad karma and hurt him in rebirth. Krishna teaches him the duties of a warrior.
He teaches him about courage, war, the nature of human life, and the role of the gods. He explains to him that his dharma (sacred duty) is to fight. Along with spiritual and mental discipline he can achieve emancipation. He fears that killing his relatives will ultimately lead him to suffering. He believes war is evil, and doesn’t want to be a part of it.In the story they talk about disciplining one’s self to overcome desire, and make ones deeds a loving sacrifice to god. When that has been accomplished, god will remove that desire. Krishna teaches this to Arjuna to help him realize that his love for his family is a worldly desire, and by killing them it’s really a sacrifice to god. Krishna helps him detach himself from his feelings and instead be lead by duty. This is what he calls “self-liberation.”
Krishna is tells Arjuna that we are indestructible because he believes in rebirth. He explains that Arjuna has to discipline his actions, by detach his self from them. One of his final lessons he teaches is to be a man of discipline. Arjuna let go of his possessions and was isolated. “A man of discipline should always discipline himself; remain in seclusion, isolated, his thought and self well controlled, without possessions or hope.” (The Bhagavad-Gita, 1023) At the end of The Bhagavad-Gita he convinces him to fight and changes his whole prospective on war.