The essence of Bhagavad Gita

Bhagavad Gita is a sermon given by Lord Krishna to Arjuna when the latter out of non-understanding wanted to escape from his duty as a warrior. Arjuna went into despair. Sri Krishna Seeing Arjuna's despair Krishna took that opportunity positively and he turned the focus of attention of Arjuna towards truth. After hearing the sutras in Samkhya yoga Arjuna started longing for truth and war became secondary though he is a warrior. So Krishna is successful to convert despair of Arjuna into longing for truth. By nature coal and diamond are made of same carbon but it is a skill to convert coal into a diamond.Krishna did that in case of Arjuna by using his alchemy of understanding. There are 18 chapters in Bhagavad Gita but Samkhya yoga, which is the yoga of understanding is the direct approach to truth. Others are meant for those who cannot understand Samkhya yoga. Lord Krishna himself declared this. So the author selected Samkhya yoga to convey the essence of Bhagavad Gita.