In the beginning of 13^th chapter, Arjuna asked for the clarification of six technical terms:  Of these six terms, Lord Krishna defines Kṣetram as the body which includes any object of experience in the creation and Kṣetrajña as the experiencer or the subject. 

Now Krishna gives simple elaboration of these two words.  What is kṣetram, what is the cause of kṣetram and what is the effect of kṣetram.  All the causes come under kṣetram, and the effects also come under kṣetram.  The entire kāriya kāraņa prabañca comes under kṣetram.  The corollary of this statement is kṣetrajña should be other than cause and effect.  The knowledge of these two alone is real knowledge. 

Verse 5

This has been taught by the sages variously.  This has been revealed distinctly through various Vedic hymns.  This has been taught through logical and well ascertained upaniṣadic statements which reveal Brahman.

Kṣetram includes the entire material world; kṣetrajña is consciousness.  The entire creation is the mixture of these two, that is consciousness and matter.  All the rishis and vedic mantras distinctly explain these two.  Consciousness is sathyam or reality and matter is mithya, and I am the consciousness principle.

Verses 6 and 7

The five subtle elements ahankara, mahat, prakriti, the ten sense organs, the mind, the five gross elements, desire hatred, pleasure, pain, the body mind complex, sentiency, fortitude – all this enumerated above briefly, is kṣetram, together with its modification.

The vedic philosophers have categorized the universe into various tattvas.  Here the universe is categorized into 24 tatvam.

1. The first basic matter principle is prakriti; potential form of universe; this prakriti is basic matter and does not have origination.  In scientific language it is the condition before big bang.
2. Mahat is the total matter in the first stage of evolution.
3. Next is Ahankara.  Ahankara is the name of total matter and not individual ego, cosmic ego.
4. 16 tatvam originate from ahankara:
   1. Cosmic mind.
   1. Ten indriyam; ten sense organs or powers of perceptions.
   1. Panca sukshma budhani; five subtle elements.
5. From the subtle elements five sthūla budhani originate

These 24 are matter or kṣetram, the inert material objects.  All these tatvam undergo constant change.  Due to the constant changes gunas are created. 

Our physical body and the mind are modification of the subtle elements so they both are matter.  The mind is an inert matter, but it has the ability to reflect the consciousness and appear to be sentient.  Reflected consciousness makes the mind appear to be sentient; this borrowed sentiency is chethana.  This reflection can exist wherever there is a reflecting medium, which is kṣetram.  So, the reflected consciousness is also kṣetram or the material universe.  The objective world created by the Lord is replaced by the subjective world created by me.  Raga and dwesha, desirable and undesirable worlds, are the result of this creation.  This results in sugam and duḥkam.  No object in the public world does produce sugam and duḥkam, however every object in my private world produces sugam and duḥkam.  Every object produces joy by arrival, and it produces sorrow by departure.  So, every object produces sugam and duḥkam.  Every undesirable object produces sugam when it departs from me and produces duḥkam when it arrives.  This capacity of this world is not intrinsic, but only because of my classification of the world as desirable and undesirable.  So, every object is not capable of producing joy and sorrow; world produces sorrow or joy only after we classify them desirable and undesirable by attaching raga and dwesha.  This list constantly changes, and lifelong struggle is to take care of this list. 

Verse 8

With verse 7, Krishna concludes the analysis of kṣetram, but he does not elaborate kṣetrajña.  He will elaborate the discussion of jñānam and purusha later.  Now Krishna comes to the third topic, jñānam from verse 8 to 12.  In these verses, jñānam means spiritual knowledge in these verse and it represents sat guna or virtue.  If these virtues are there, self-knowledge is automatically obtained.