Bhagavad Gita Chapter 2, Verse 30

देही नित्यमवध्योऽयं देहे सर्वस्य भारत | तस्मात्सर्वाणि भूतानि न त्वं शोचितुमर्हसि ||

dehī nityam avadhyo 'yaṁ dehe sarvasya bhārata tasmāt sarvāṇi bhūtāni na tvaṁ śocitum arhasi

The Self dwelling in the body of all beings is eternally indestructible, O Bharata. Therefore, you should not grieve for any creature.

Krishna concludes his teaching on the Self with a radical expansion: the dehī (embodied consciousness) isn't just indestructible—it's universal. 'Dehe sarvasya' (in the body of all) means the same consciousness inhabits every being. Arjuna's consciousness and Bhishma's aren't separate entities but one awareness appearing as two, like the ocean appearing as many waves. This is Advaita (non-dualism): many bodies, one consciousness. Therefore—'tasmāt sarvāṇi bhūtāni na tvaṁ śocitum arhasi'—you shouldn't grieve for any being. Not because they don't matter, but because what they fundamentally are cannot be harmed. Bodies change; consciousness doesn't.