It is the salivation of our existence and even the source of joy. The word from this is dharma reason. The Bhagavad Gita is great because embodies the reasoning mind capable of choosing the way or purpose over the automaticity of our life. Leads by desire. If Arjuna simply follows his desire not to fight, he learns nothing. Instead, Krishna tells him to fight the God. This is his duty, his purpose, his dharma, and it changed the way he was believing and wants to be