Any way the subject matter of this spiritual energy exhibited by the living being is undoubtedly very complicated thing for an ordinary man. The ordinary man is therefore astounded in the subject. Sometimes he partially understands it through the imperfect senses and sometimes he fails to know it altogether. The best thing is therefore to hear the grave subject matter from the highest authority Sri Krishna or His devotee representative coming down in the chain of disciplic succession. Bhagavad-gita is the essence of all the Upanisads and Vedanta.