Second episode/adhyaya – Sankhya yoga
antavanta ime dehā
antavantaḥ—perishable; ime—all these; dehāḥ—material bodies; nityasya—eternal in existence; uktāḥ—it is so said; sarīriṇaḥ—the embodied souls; anāśinaḥ—never to be destroyed; aprameyasya—immeasurable; tasmāt—therefore; yudhyasva—fight; bhārata—O descendant of Bharata.
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Even the body of the embodied (soul) who is said to be nitya(eternal), anashina(indestructible), aprameya(ananta/immeasurable) is perishable. Therefore fight, O Bharatha!
Body will perish. It is meant to be perished. You cannot save it how much ever you want. Even though the soul is indestructible, eternal, and immeasurable, the material body is not. Hence fight O Arjuna!
Continuing thought from the previous verses, Sri Krishna is saying Arjuna not to cry over something(body) that is bound to perish. The soul is not destroyed anyways.