|Chapter 2: Contents of the Gita Summarized|
atha cainam nitya-jatam
nityam va manyase mritam
tathapi tvam maha-baho
nainam socitum arhasi
If, however, you think that the soul [or the symptoms of life] is always born and dies forever, you still have no reason to lament, O mighty-armed.
Krishna so far has explained things to Arjuna from the perspective of the scriptures. In this verse, He presents a new line of thought (indicated by the phrase "If, however"). Just in case Arjuna were to subscribe to the atheistic philosophy that the body is simply a bag of chemicals, then still Arjuna should do his duty – after all what is the harm is destroying a bag of chemicals? Thus if Arjuna were to accept the sastric perspective that the soul is eternal – then no one will really die on the battle field. If he were to accept the atheistic perspective that there is no soul then there is no sin in destroying a bag of chemicals. In either case Arjuna should do his duty and fight. Krishna thus checkmates Arjuna from all angles. Krishna addresses Arjuna as Mahabahu (O might armed) in a sarcastic note here. Mahabahu is another term for ksatriya, and a ksatriya is a person who has read and understood the Vedas. Thus Krishna is sarcastic in calling Arjuna a ksatriya even if he does not accept the sastric view point that life come from the soul and not the combination of matter.
Please read the Sanskrit Verse and the Prabhupada's Purport.