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.
I shall speak of that which is to be known, by realizing which one attains Immortality. The supreme Brahman is without any beginning. That is called neither being nor non-being.OPEN VERSE
That (Knowable), which has hands and feet everywhere, which has eyes, heads and mouths everywhere, which has ears everywhere, exists in creatures by pervading them all.OPEN VERSE
Shining through the functions of all the organs, (yet) devoid of all the organs; unattached, and verily the supporter of all; without quality, and the perceiver of qualities;OPEN VERSE
Existing outside and inside all beings; moving as well as non-moving, It is incomprehensible due to subtleness. So also, It is far away, and yet near.OPEN VERSE
And the Knowable, though undivided, appears to be existing as divided in all beings, and It is the sustainer of all beings as also the devourer and originator.OPEN VERSE
That is the Light even of the lights; It is spoken of as beyond darkness. It is Knowledge, the Knowable, and the Known. It exists specially in the hearts of all.OPEN VERSE