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.
Arjun said: O Keshav, I wish to understand what are prakṛiti and puruṣh, and what are kshetra(field) and kshetrayajna(knower of the field)? I also wish to know what is true knowledge, and what is the goal of this knowledge?OPEN VERSE
The Blessed Lord said: O son of Kunti, this body is referred to as the 'field'. Those who are versed in this call him who is conscious of it as the 'knower of the field'.OPEN VERSE
And, O scion of the Bharata dynasty, under-stand Me to be the 'Knower of the field' in all the fields. In My opinion, that is Knowledge which is the knowledge of the field and the knower of the field.OPEN VERSE
Hear from Me in brief about (all) that as to what that field is and how it is; what its changes are, and from what cause arises what effect; and who He is, and what His powers are.OPEN VERSE
It has been sung of in various ways by the Rshis, separately by the different kinds [The different branches of Vedic texts.] of Vedic texts, and also by the rational and convincing sentences themselves which are indicative of and lead to Brahman.OPEN VERSE