I do not wish to kill these, even if they kill me, oh Madhusūdana; what to say of the kingdom of the three worlds, what less for the earth?

The argument reaches its extreme: ghnataḥ api (even if they kill). Arjuna would rather die than kill. This is the ahiṃsā (non-violence) stance in its most absolute form.

Madhusūdana (slayer of Madhu, a demon) is a warrior epithet of Kṛṣṇa, ironically used in a moment of rejection of violence. The cosmic scale: trai-lokya-rājyasya (of the kingdom of the three worlds: heaven, earth, underworld) against mahī (the earth alone). If not even for the kingdom of three worlds, how for mere hectares?

Kiṃ nu (what less, what to say?) is a rhetorical figure of adhyavasāya (extreme concession). The nu is emphatic, almost exasperated.