Everything contained in Bhagavad Gita, the sermon of Lord Krishna to Arjuna is allegorical. Krishna agreed to give sermon of Bhagavad Gita to Arjuna only when he succeeded reaching state of enlightenment. What this means in simple terms?
Only after reaching state of enlightenment Arjuna realized from within that expressing cowardice when facing enemy was not practicing Dharma (righteousness). Lord Krishna is soul atman, the spirit existing in all human beings.
In case of Arjuna, the Pandavas the battle of Mahabharata was no ordinary war; it was a battle that was to be fought to re-establish Dharma (righteousness) against evil forces of adharma (lawlessness).
Every single moment in human beings both positive and negative thoughts clashed resulting in a battle of Mahabharata within every second of life. This is termed Samudra Manthan in Hinduism.
The battle of Mahabharata, Samudra Manthan produces both Amrita (elixir of life) and Vish (poison). Seekers, those indulging in spirituality used Amrita to awaken kundalini shakti fully. Those satisfied with materialistic pursuit of life had to drink Vish again and again resulting in multitude sufferings, sorrows time and again.
When a seeker indulging in spirituality encountered Vish, he instead of drinking it retained it in the neck, prime reason why body of both Lord Shiva and Krishna is depicted as dark blue in color. The serpents around the neck of Lord Shiva depict a seeker, traveler of spiritual path finally succeeding in full awakening of kundalini shakti. The neck of Lord Shiva and Krishna is sometimes depicted dark blue in color which results from retention of Vish (poison).
Moksha is the state reached after gaining enlightenment, state of self realization, god realization. Arjuna must have definitely reached state of moksha in his lifetime.
Whenever a human being on mother earth succeeds reaching state of enlightenment, state of self realization, god realization the entire wisdom of Bhagavad Gita automatically gets disclosed to one. One finally becomes knower of all and everything contained in Bhagavad Gita and also Upanishads (independent spiritual treatises) becomes like ABCD.
Lord Krishna is never found externally. Lord Krishna always exists in us as our soul atman, the consciousness within existing in heart.
The sole purpose of human life on mother earth is reaching stage of self realization, god realization so that soul atman within could reach state of absolute purity, finally liberating self from cycle of birth and death forever.