देही नित्यमवध्योऽयं देहे सर्वस्य भारत ।
तस्मात्सर्वाणि भूतानि न त्वं शोचितुमर्हसि ।।
dehī nityamavadhyo'yaṃ dehe sarvasya bhārata ।
tasmātsarvāṇi bhūtāni na tvaṃ śocitumarhasi ।।
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Amongst Atmas, there are no divisions (like some are perishable & others aren't). Even when deha is destroyed, Atma is not. The differences amongst Atmas arise only via their karma-phalas..
Once karmas are destroyed, all Atmas are one & the same..
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Oh bharata kula born Arjuna, your worries are mis-placed (on killing bhishma/drona et al..)
Even when all living beings in this earth are destroyed, Atma remains eternal, pure, undecaying & imperishable.
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The primary amongst 4 types of deha (bodies) is svarupa deha. It deha has no beginning or end & is eternal. It has all parts/organs of body but in purest form
Based on the nature of this sublime svarupa deha, jivAtmas are classified as follows
2. aniruddha deha - This covers the linga deha & specifically belongs to paramAtma Himself. It gets dissolved only during pralaya
All these 4 types of dehas are protected by Me. So you don't worry about killing your enemies. Plunge into the battle, Oh bhaarata!!