Krishna has just argued that the self (atman) is eternal and cannot be killed. Now he offers a second argument for those who aren't convinced: even if you believe the self is not eternal, grief is still irrational.
atha cainaṃ nitya-jātaṃ nityaṃ vā manyase mṛtam | tathāpi tvaṃ mahā-bāho nainaṃ śocitum arhasi ||
But even if you believe this self (atman) is perpetually being born and perpetually dying, O mighty-armed (Arjuna), even then you should not grieve for it.
Some people cannot accept the idea of an eternal, unchanging self. It feels too abstract, too metaphysical. Krishna acknowledges this. His second argument works even for someone who rejects his first. This is smart teaching: he does not require belief before offering clarity.
If everything is impermanent, then death is not a tragedy to be grieved, it is just the nature of things. The materialist view of reality, taken seriously, does not produce grief. It produces acceptance. Arjuna is holding a materialist-ish assumption (these people will be gone) but drawing a non-materialist emotional conclusion (this is unbearable). Krishna is pointing out the inconsistency.
Krishna is not scolding Arjuna. He is pointing out that the reasoning behind the grief does not hold. Whether the self is eternal or not, grief over what must happen is a category error. This is important: the critique is intellectual, not moral.
Arjuna might have thought: 'Fine, I don't buy the eternal soul argument, so grief is still valid.' Krishna shuts that door here. He is being thorough. He wants Arjuna to see that there is no philosophical position from which prolonged, action-paralyzing grief is justified in this situation.
Person A is stuck because they believe the thing they are afraid of losing is permanent and precious, and the loss will be permanent and devastating. From that stance, hesitation and grief feel proportionate and justified. Person B has sat with the same fear and run both versions: if life is short and bodies die, then clinging to things staying the same is already a lost bet. And if there is something in a person that does not die, then the fear is also groundless. Either way, they take action. The paralysis dissolves not because they feel better, but because neither logical path supports staying frozen.
Arjuna is slumped, overwhelmed, refusing to act. Calling him 'great-armed' at the end of this tight logical argument is a quiet prod: your hesitation is inconsistent with your actual nature and capacity. Krishna is not just arguing; he is also addressing the identity that has temporarily gone offline.
Verse 2.27 deepens the impermanence argument: for one who is born, death is certain, and for one who dies, rebirth is certain. Therefore grief over the inevitable is simply not the right response. When ready, say: "2.27"