Arjuna draws a line that nothing can cross. He tells Krishna: O Madhusudana, I do not wish to kill these people — even if they try to kill me. I would not do it for the sovereignty of all three worlds. So what to speak of this small earth?
The scale of his refusal is striking. Three worlds — heaven, earth, and the netherworld — represent the ultimate prize in the Vedic worldview. Arjuna is saying that no reward in all of existence could make this killing acceptable to him. A mother would never harm her child, no matter what the child has done. Arjuna's love for his kinsmen runs that deep.
This verse reveals the full depth of his compassion. He is a warrior who has won countless battles, who wields the great Gandiva bow — and yet his heart is so full of love that he would rather accept death than cause harm to his own family.