If we examine dharma as a form of duty, it becomes imperative to understand it as the key to unlocking the meaning of the work. The role of dharma is evident in much of the epic. This is particularly true for Arjuna. When the son of Kunti feels despair and forlornness at the battle that lies in front of him, he abandons his dharma. It is his dialogue with Lord Krishna that reminds him of the power of dharma. The idea of fulfilling one's duty is vitally important to the work. Krishna uses the construction of dharma to enable Arjuna to realize what the right thing to do actually is.
Dharma becomes the critical ingredient to understanding the meaning of the epic. One achieves liberation from the pain in this life through relegating one's thoughts to duty. Lord Krishna teaches Arjuna that dharma is real, and all else is unreal. When we as individuals understand this element, Lord Krishna reveals to Arjuna that all else can fall into its appropriate context. It is for this reason that dharma is so important to the work. The entire reason for the struggles of the Pandavas is because of a lack of order, a chaos that has enveloped ethical conduct. Lord Krishna is the reminder that adherence to dharma is the only way in which one can evade the pain of loss, the struggle of this life ("samsara").
Lord Krishna says this much to Arjuna, revealing the power of dharma in the work, in general:
Giving up all vexations and paths, do thou take refuse unto Me. I will save you from all dangers.
It is this construction of dharma that enables Arjuna to fight, carrying out his Dharma. It is also this construction that brings the power of the work into the full light of meaning for the reader, who is like Arjuna himself in the struggle of this life.