But if you believe that this is constantly being born or constantly dying, even so, oh mighty-armed one, you should not grieve in this manner

Kṛṣṇa offers an alternative argument for one who does not accept the immortality of the ātman. Atha (but, if) introduces the condition: manyase (you believe/think) that this is nitya-jātam (always being born) or nityaṃ mṛtam (always dying) — the Buddhist position of constant anitya (impermanence).

Tathāpi (even so) — even under that hypothesis, na śocitum arhasi (you are not worthy of grieving). The logic: if death is inevitable and ceaseless, why grieve what is inevitable?

Mahābāho (of mighty arms) — the warrior epithet is now used without irony. Arjuna is fit for battle, not for weeping.