Shree Bhagavaan uvaacha:
idam shareeram kaunteya kshetramityaabhidheeyate |
etadyo vetti tam prahuhu kshetrajnya iti tadvidaha || 1 ||

Shree Bhagavaan said:
This body is defined as the “field”, O Kaunteya, and he who knows it is called the “knower of the field”, in this manner, by the knowers of both.

idam : this
shareeram : body
kaunteya : O Kaunteya
kshetram : field
iti : in this manner
abhidheeyate : defined as
etat : it
yaha : which
vetti : knows
tam : he who
prahuhu : call
kshetrajnya : knower of the field
iti : in this manner
tadvidaha : knowers of both
As we commence the thirteenth chapter, let us take stock of where we have come so far in the Gita. In the first six chapters, Shri Krishna focused on revealing the true nature of the individual self, what we refer to as “I”. In the first chapter, Arjuna was caught in a web of grief and delusion because he considered himself as a body that is attached to its friends and family. Shri Krishna revealed to Arjuna that his nature was the infinite eternal essence and not the body. He then guided Arjuna step by step through the means of arriving at this understanding starting with karma yoga, then karma sanyaasa yoga, and finally dhyaana yoga. Only in meditation can we experience the true nature of our “I” as the “saakshi” or witness of our body, mind and intellect.
In the next set of six chapters, Shri Krishna focused on revealing the true nature of the world we live in. We usually think of the world as comprised of matter in various forms. Shri Krishna revealed to Arjuna that this world is comprised not only of matter, but also of spirit or life-giving consciousness. These are also known as the lower and higher aspects of Prakriti or nature, respectively. He then revealed that Prakriti is nothing but a shakti or power of Ishvara himself, and therefore Ishvara is in all, and all is in Ishvara. He is the material cause or the raw matter, as well as the efficient cause or the intelligence that has created the universe. The true nature of the world is Ishvara who is the “adhishthaana”, the foundation or the substratum of the world.
Having revealed all of this, why do we need six more chapters? Let us proceed step by step, since we will be delving into new waters. Our antahakarana or inner instrument comprising the mind, intellect, ego and memory comes with three inbuilt defects. “Mala” or dirt comprises our stock of unfulfilled desires. “Vikshepa” is the tendency of the mind to jump from one thought to another. “Aavarana” is the veiling or covering that hides the understanding of the true nature of the self, of who we are in essence. Karma yoga helps remove the defect of mala by extinguising selfish desires to a great extent. Bhakti yoga helps remove the defect of vikshepa through single-pointed devotion of Ishvara. However, we will never achieve complete self realization unless we tackle the third defect of Aavarana. That is the purpose of the last six chapters of the Gita.
How do the last six chapters remove this defect of aavarana or veiling? This can happen only when we intuitively understand the true meaning of the “mahaa vaakyas” or great statements that have been revealed in the Vedas. The Gita reveals the mahaa vaakya “Tat Tvam Asi” which means “You Are That”. The first six chapters of the Gita revealed the nature of “Tvam” which means “You” as the saakshi or witness, and the next six chapters revealed the true nature of “Tat” which means “That” as Ishvara, the adhishthaana or foundation. The last six chapters reveal “Asi”, the identity or the equality between the real nature of “You” and “That”. Shri Krishna knows that this topic may be somewhat tough to understand, so he addresses Arjuna as “Kaunteya”, one whose intellect is as sharp as a knife or “kunta”, so that he remains sharp and alert throughout this chapter.
Now, let us look at the first shloka. The term “shareera” or body is used in a general sense to refer to the three bodies that we are made up of: the physical body, the subtle body (the mind, intellect, ego, memory and the physiological functions) and the causal body (our vaasanaas or unfulfilled desires). In other words, anything that is temporary, changing and perishable is referred to as “this body”. Shri Krishna says that anything that we term as “this body” is defined as the “kshetra”, the field. But there is something in us which is changeless and knows that it is different from the ever-changing field. This intelligence principle in us, this consciousness is termed as the “kshetragnya”, the knower of the field. Both these terms are defined by the knowers of both the field and its knower, in other words, great seers and sages.
Why do we need to know such esoteric terms? Shri Krishna uses these terms to lay the groundwork for the next shloka, which is one of the most important shlokas in the Gita. He wants to give a foundation that we can use a spring board to leap into the next shloka.