अन्तवन्त इमे देहा नित्यस्योक्ताः शरीरिणः।
अनाशिनोऽप्रमेयस्य तस्माद्युध्यस्व भारत।।2.18।।
These destructible bodies are said to belong to the everlasting, indestructible, indeterminable, embodied One. Therefore, O descendant of Bharata, join the battle.
Now what is that ‘asat’ which changes from its own existence?
These bodies (plural) are subject to end i.e. these bodies are destructible. And these bodies belong to the embodied shariri (singular!!), the one which is within the body. This shariri is atman and it is eternal i.e it never ends and it is indestructible. Just as we have sat-buddhi (i.e. the cognition related to sat) in mirage but when contradicted with pramanas (proof—means of knowledge), that sat-buddhi in mirage ends, similarly the sat-buddhi in these bodies ends like that of the bodies in dream or created by magician.
Objection: Why did Bhagvan use both anashinah (indestructible) and nitya (eternal) for shariri (=atman=embodied)? Are they not superfluous because both indicate the same thing?
Answer: Destruction is of two types. One is complete non-perception. Like the destruction of these bodies after death. Another is when the bodies degenerate due to some illness, disease etc. Since atman is stated to be nitya and anashinah, Bhagvan explains that atman has neither kind of destruction. Had he not told this, it would have amounted to eternity of atman in the same manner as that of elements like prithivi etc.
Further, atman is aprameya i.e. one which cannot be known from any praman i.e. means of knowledge. There are five sources of knowledge. They are pratyaksha (direct perception), anumana (logic), upaman (comparison), arthapatti (circulstantial inspection) and Vedas. Atman cannot be known through either of them and hence it is aprameya, indeterminable.
Objection: But atman is known through Vedas (earlier one erroneously believed it to be known through pratyaksha etc.). How do you say that atman is aprameya?
Answer: Because atman is self-evident. Only when one is established as pramata (knower) upfront, he starts looking for pramana (means of knowledge) and prameya (object which is to be known). Atman is not something which is not well-known. It is pretty much already known. Only when one ascertains oneself as ‘I am so and so and I am such and such’ that one starts looking for the objects which are to be known. Thus, it is obvious that atman is self-evident and no means of knowledge are required to know it.
Objection: Then what are these Vedas and shastras for? What do they do if atman is already known?
Answer: Even though atman is self-evident and already known, we don’t know its real nature. I feel myself (=atman) to be limited whereas atman is actually unlimited. So shastra is a praman in so far as it removes the misconceptions about atman. It is a final means of knowledge for removing the superimposition of non-atman into atman. Shastra is not agyat-gyapak means it does not reveal something which is unknown in so far as atman is concerned (for things like heaven, yajna, punya etc, shastra is agyat-janapak). And there is shruti also—the Brahman which is immediate (saakshaad) and not-indirect (aparoksha), is the atman of all (Brihadaranyak).
Since atman is such non-doer and eternal, there is no point in not fighting and you must fight.
Objection: Is Bhagvan enjoining Arjuna to fight? Is Gita a pravritti-shastra (providing injunctions about karma)?
Answer: No. Gita is a nivritti-shastra. Arjuna was ready for war. Due to shoka-moha, he did not want to fight. So Bhagvan was preaching this nivritti-shastra to remove the shoka-moha. (Smritis like Manu Smriti etc. which define the karmas for respective varnas are pravritti-shastra and in accordance with them, Arjuna was ready to fight).
In order to give evidence therefor, Bhagvan quotes two hymns from Shruti.
Your thinking that Bhishma, Drona etc will be killed by you and that you will be their killer is false and wrong. How? [in next shloka]