अथ चैनं नित्यजातं नित्यं वा मन्यसे मृतम्। तथापि त्वं महाबाहो नैवं शोचितुमर्हसि ॥

atha chainaṁ nitya-jātaṁ nityaṁ vā manyase mṛitam tathāpi tvaṁ mahā-bāho naivaṁ śhochitum arhasi

Or if thou thinkest of him as being constantly born and constantly dying, even then, O mighty-armed, thou shouldst not grieve.

In plain words: Krishna says that even if Arjuna thinks the soul is always being born and always dying, he still should not grieve.