Metaphorically Krishna and Arjuna in the battlefield before the Mahabharata war represents state of a seeker of the level of Swami Vivekananda facing the enemy head-on. Arjuna is in total dilemma, outwardly he has to fight the enemy but inwardly he also indulged in quest for truth. It is in those moments he finally realizes the cosmic truth when Lord Krishna, his soul atman existing in heart dictates, guides him from within.
When facing the enemy as a Pandava Prince Arjuna feigned cowardice. He did not want to fight the war as the enemy consisted of his close cousins, close relatives and friends, even maternal grandfather Bhishma Pitamah and Guru Dronacharya. But finally inner sense prevails and he realizes from within that he was only an instrument in hands of God Almighty doing his bidding. Arjuna realizes that the ultimate master and controller of his body was a soul atman.
When Arjuna realizes he was only a medium for soul atman within to cleanse itself of dross impurities within and life truly did not belong to the manifest physical body he prepares himself to fight. Arjuna also realizes that being a soul atman he was immortal but to gain immortality he just could not express bondage, earthly ties towards his arch enemies. For a soul atman there was never any earthly relationship whatsoever.
Earlier Arjuna was looking at the war and his enemies from a personal angle, from the medium of his body, earthly ties but he finally realizes that it was not for his own self but all his countrymen and soldiers that we had to fight the enemy head-on. As the battle of Mahabharata was a battle of Dharma (righteousness) Arjuna had to win it under all circumstances and cost. As Krishna is denoted as Dharmaraja and with Dharmaraja on his side the Pandavas finally won the war!
Dharmaraja stood for a seeker who had finally realized self, reached stage of enlightenment. It is in those moments Arjuna realizes his cosmic swaroop that he was a soul atman and not the body.
The sermon of Krishna to Bhagavad Gita is a treatise primarily explaining that one is a cosmic traveler, a spirit manifesting human form. And for a spiritual being there was no reason for not fighting. Arjuna succeeded in reaching state of enlightenment in the battlefield itself. The moment he became an enlightened one, he prepared himself to fight the enemy head-on. For an enlightened one no relationship of any kind could ever exist on mother earth. The state of enlightenment is reached after cutting all earthly ties forever.
For human beings in search of hidden values of life, in search of God assimilation of pearls of wisdom contained in Bhagavad Gita is an absolute must, one cannot do without!