In Mahabharata Krishna is portrayed as a shantidoot (messenger of peace). Why?
Metaphorically Krishna in Mahabharata stands for a pure soul atman that manifested human body.
Arjuna from the very beginning was a spiritual person. In the battle of Mahabharata when facing his arch enemy Kauravas that consisted of his maternal grandfather Bhishma Pitamah, Guru Dronacharya, close cousins relatives and friends… he refused to fight and feigned cowardice.
As Arjuna was the chieftain of his army and also represented all country men, he was extremely perturbed internally but unable to decide what to do in the circumstances. And at that very moment he reached state of enlightenment. The moment enlightenment took over Arjuna realized the shallowness of manifest physical life. He realized he was primarily a spiritual traveler manifesting human body and death should carry no meaning for him.
His contemplation (chintan) on the spiritual precepts of life had finally come to an end. He was able to take a final call; he decided to fight the enemy head-on. Despite being an enlightened soul, he prepared himself to fight the enemy. Why?
The battle of Mahabharata is no ordinary battle. The battle of Mahabharata was fought to defeat evil forces and re-establish Dharma (righteousness). Whenever society reaches its lowest ebb, a point of no return… a battle of Mahabharata, mother of all wars is the only solution. The battle of Mahabharata was fought in Dwapar Yuga, in periods of extremist strife, tribulation.
In present times we are passing through Kali Yuga, the darkest hour of the night. To annihilate dark forces of nature, in present mankind awaits advent of Kalki Avatar, one possessing powers almost equivalent of Lord Krishna. This one-man army would be able to achieve the unachievable and finally succeed establishing Dharma (righteousness) and start Satyuga (Golden period).
All enlightened souls are always considered messengers of peace. Mahavira, Gautama Buddha, Jesus Christ and Prophet Mohammed Al were passengers of peace and so was Arjuna. But in times of Arjuna it was not a period of ordinary strife, Dharma had to be established at all costs. And finally Arjuna agreed to fight.
In the battle of Mahabharata Arjuna reached a state of truthfulness to the extent he realized god. The Krishna within activated fully meaning Arjuna became Krishna, an enlightened one coupled with powers of Chanakya (the most able administrator in the entire history of mankind). Thereafter it was never looking back. The liberated soul atman of Arjuna existing in his heart goaded him to start battle of Dharma wholeheartedly and so did Arjuna.
For Arjuna, listening to the voice of Krishna from within was no more difficult. Remaining truthful he could distinctly hear voice of Krishna coming from within. Mounted with power of Krishna, the liberated soul Arjuna thrust himself fully in the war.
In the initial stages of war Arjuna and his brothers acted as shantidoots (messengers of peace) but the camp of Kauravas consisting of Duryodhana and others was not prone to reason. No matter how many times Arjuna tried to convince Duryodhana not to indulge in a war of epic proportions, but Duryodhana was not only prepared to fight Pandavas but also felt confident he would win the war.
Preaching ahimsa (nonviolence) when facing the enemy is not the right thing! For the death of Lala Lajpat Rai, who was mercilessly beaten by British Mahatma Gandhi is squarely to blame and for this act of his God shall never forgive Mahatma Gandhi.
The ultimate message conveyed by Krishna in Mahabharata is the importance of travelling spiritual path. Doing so one finally liberates self from cycle of birth and death forever becoming a pure soul atman in the cosmic journey of life.