Chapter 2,Verse 26

atha chainam nithyajaatham
nithyam va manyase mrutham
tathapi tvam mahabaho
nivam shochitum arhasi

From verses 26 to 28,Lord Krishna takes a different approach in preaching to Arjuna.
All along,he was trying to impress upon Arjuna that he is not the visible human bpdy,but the atma.In these verses,Krishna makes a suppositional argument that everyone were their mere visible mortal human bodies.He says that,even if Arjuna considered atma to be mortal,people have come with a date of birth and will have a date of death,he must not grieve over the inevitable.