Everything contained in Bhagavad Gita is allegorical. Arjuna was a spiritual traveler from beginning of life. In the midst of battle of Mahabharata while contemplating on vital issues of battle he suddenly reached stage of self realization, god realization. This happened because he gave more preference to voice of Lord Krishna coming from within than his own ego.
Lord Krishna is our soul atman existing in heart. One can hear voice of Lord Krishna from within if we demolished our ego in totality and this is exactly what Arjuna did. In the initial stages of battle Arjuna was greatly confused how to fight his enemy that included close cousins, relatives and friends and even maternal grandfather Bhishma Pitamah and Guru Dronacharya.
The moment Arjuna reached state of enlightenment; he realized he was primarily a soul atman and not the manifest physical human form. The fear of death of his cousins, close relatives and friends’ even maternal grandfather and Guru evaporated forever. Realizing he was only a trustee doing bidding of God Almighty Arjuna finally prepared to fight the enemy head-on.
For an enlightened one fear of death meant nothing. Furthermore Arjuna realized the battle of Mahabharata was no ordinary battle but to re-establish Dharma (righteousness). As Arjuna represented his countrymen and soldiers, the personal feeling of fighting his relatives vanquished forever. Arjuna re-energized himself and shed all cowardly behaviour behind.
Indulging in spirituality from the beginning of life Arjuna was supposed to reach state of self realization but when he did not know. Fortunately for him he reached state of enlightenment before the start of battle. Thereafter it was never looking back.