In this Chapter Bhagavan Krishna explains clearly about the difference between the atman and anatman.  The name of this chapter itself is Kshetra kshetrajna vibhaga yoga:  Kshetram is the field and kshetrajna is the knower of the field. Kshetra is anatma and Kshetrajna is Atma.  The body and mind, senses are the anatman and the knower of that is Atma.

The knower of the field, kshetrajnan is universal whereas, the fields are diverse.  The field has many modifications-like the elements, egoism, intellect, senses, desire, hatred, pleasure, pain, intelligence etc.  what are all knowable belongs to kshetra

Knowledge makes one to know the kshetrajna.  That leads one to knowledge are humility, unpretentiousness, non-injury, forgiveness, uprightness, service to the teacher, purity of the mind, Steadfastness, self-control, balanced mind towards duality, absence of egoism, worry of birth, death, old age, sickness and pain, non-attachment towards worldly objects, unswerving devotion to the lord, constancy in self-knowledge, all these leads one to Jnana, the kshetrajna.  That which opposes all this is ignorance.

Bhagavan Krishna says that I will declare what is to be known, knowing which one attains immortality.  There is only one common consciousness in all beings. That common consciousness is eternal, self-luminous and all-pervading. That common consciousness is Para Brahman.  It is undivided yet it exists as if divided in beings. It is known to be the support of all beings.  It is the light of all lights and is said to be beyond darkness.  One who knows this and identifies with it attains the supreme.

The individual soul which is the reflection of the supreme consciousness identifies with nature and it experiences both pain and pleasure; and it takes consecutive births in the good as well as in the evil wombs.  Actually, the supreme soul in the body is the spectator, the great Lord, and the supreme Self.  A person who knows the difference between the Atman (Supreme soul) and matter is not perturbed in any situation and he does not take rebirth.

To behold the self in the self by the self there are many methods.  One can behold it by bhakti (very common). One can behold it by meditation, by knowledge, by action etc. whatever being is born in this world, whether living or non-living it is the union between the atma and anatman or the field and the knower of the field.

Bhagavan says that He sees, who sees the supreme Lord existing equally in all beings, he sees the unperishing within the perishing.  When he sees the self instead of seeing the body, then he does not destroy the self by the self. He goes to the highest goal.  Gradually he understands that all the actions are performed by nature and the self is actionless.  He sees that all the beings are resting in the One.  That supreme being devoid of any qualities, imperishable, though dwelling in the body -it neither acts nor is tainted.  Just like how the one sun illumines the whole world, that supreme Self, illumines the whole field.

Bhagavan says that one who perceive the distinction between the field and the knower of the field go to the supreme.