How is the story of Arjuna and Krishna a perfect metaphor for understanding the importance of karma and reincarnation?
One way in which Lord Krishna relieves Arjuna of his existential crisis of responsibility is to remind him of how karma and reincarnation is part of the submission to the divine in which the pain of this life can be minimized. For Arjuna, the pain of this life is something of which he does not understand the full implications. The pain that he confesses to Lord Krishna is what he experiences in this life. The agony he experiences at what he must do is because he believes that his totality is in this life. It is here where Lord Krishna reminds Arjuna that this life is merely a part of a larger journey. The soul is what is immortal. This is the real. A soul that has submitted itself to carrying out its mission in accordance to Lord Krishna is one that undergoes birth and rebirth. Lord Krishna teaches this to Arjuna, that the duty he must perform now is a result of the karmic configuration that guides his being. When Arjuna is able to submit his will to Lord Krishna, seeing that his soul is aligned to his wishes, Arjuna is able to understand that performing his duty is part of his being. The karma that one must "work off" in each birth is where reincarnation is a part of existence until spiritual liberation at the feet of Lord Krishna is evident. Lord Krishna teaches Arjuna to not dwell on the pain and suffering of this life, for this is one of many. The pain experienced in this life is not "the real," as opposed to understanding the nature of the soul's being as realized through karma and reincarnation. It is for this reason that the story of Arjuna and Lord Krishna becomes one of the most fitting understandings of karma and reincarnation. It is through their exchange that the reader understands that they, too, are like Arjuna with the struggles they face in their own lives. It is perfect because when Krishna is talking to Arjuna, it is almost as if he is talking to us, as well.