The thirteenth chapter of the Bhagavad Gita is Ksetra Ksetrajna Vibhaaga Yoga. The word kshetra means the field, and the kshetrajna means the knower of the field. We can think of our material body as the field and our immortal soul as the knower of the field. In this chapter, Krishna discriminates between the physical body and the immortal soul. He explains that the physical body is temporary and perishable whereas the soul is permanent and eternal. The physical body can be destroyed but the soul can never be destroyed. The chapter then describes God, who is the Supreme Soul. All the individual souls have originated from the Supreme Soul. One who clearly understands the difference between the body, the Soul and the Supreme Soul attains the realization of Brahman.
Thus has been spoken of in brief the field as also Knowledge and the Knowable. By understanding this My devotee becomes qualified for My state.OPEN VERSE
Know both Nature and also the individual soul to be verily without beginning; know the modifications as also the qualities as born of Nature.OPEN VERSE
With regard to the source of body and organs, Nature is said to be the cause. The soul is the cause so far as enjoyer-ship of happiness and sorrow is concerned.OPEN VERSE
Since the soul is seated in Nature, therefore it experiences the qualities born of Nature. Contact with the qualities is the cause of its births in good and evil wombs.OPEN VERSE
He who is the Witness, the Permitter, the Sustainer, the Experiencer, the great Lord, and who is also spoken of as the transcendental Self is the supreme Person in this body.OPEN VERSE