Human beings want to be happy as long as they are alive. Even after death we want to be happy. Gita deals with the subject of what is happiness, how to remain happy even in the midst of challenging situations. Like we use google maps (gps) to reach a destination, if we have Gita Practising System (GPS) we will be able to reach the destination easily. Gita is like a road map of happiness.
Arjuna was not happy in doing his duty as a warrior. He realised that even if he gets the kingdom without any enemy and without any borders, or even the kingship of heavens, that will not make him happy. Irrespective of the preparations for the war all throughout his life he realises that it is not the goal of his life. That was his question. “How can we be happy killing my own people? (कथम् सुखिनः स्याम माधव ?) Oh Lord please show me the path to permanent happiness. I seek your help. Please guide me” (यत् निश्चितं श्रेयः स्यात्, तत् मे ब्रूहि । अहं ते शिष्यः । त्वं प्रपन्नं मां शाधि ।).
Arjuna understood that by his action he was neither happy then nor will he be happy in the future. In the past also the Pandavas had had only sufferings. So how to be happy was his question. Hence Sri Krishna’s answer is in those lines. The answer to finding permanent happiness is the Bhagavad Gita.