Now Krishna draws the practical conclusion from everything he has taught so far. These bodies are perishable — they will end. But the soul that dwells in them is eternal, indestructible, and immeasurable. Therefore, O Bharata — fight.
The word 'aprameya' deserves attention. It means immeasurable — beyond the reach of any instrument or method of measurement. The soul cannot be weighed on a scale, seen under a lens, or bounded by any number. It is not merely very large or very old. It is beyond the category of measurement entirely.
The command 'yudhyasva' — fight — arrives not as a bare order but as a logical consequence. If the soul cannot be killed, then Arjuna's central fear — that he will destroy his loved ones — is based on a misunderstanding. Krishna is not telling Arjuna to ignore his feelings. He is telling him that the premise behind those feelings is wrong.