B.G 2.12
na tvēvāhaṁ jātu nāsaṁ na tvaṁ nēmē janādhipāḥ। na caiva na bhaviṣyāmaḥ sarvē vayamataḥ param ॥ 2-12॥
Never was there a time when I did not exist, nor you, nor these princes. Surely not, shall we all ever cease to exist hereafter.
Gīta Tātparya 2.12
God has no destruction of the body or the self. The individual self is indestructible, but its body goes through destruction.
bandhusnēhāddhi tvayā svadharmanivr̥ttiḥ kriyatē। tatra dēhanāśabhayāt kiṁ vā cētananāśabhayāt? dēhasya sarvathā vināśitvānna tatra bhayē prayōjanam। na ca cētananāśabhayāt। tasyāvināśitvādēva। na tāvatparamacētanasya mama nāśōsti। ēvamēva tavānyēṣāṁ ca।
Because of friendship of relatives, you are forsaking your own duty (sva-dharma). Is this because of the fear of destruction of their body, or their self? There is no use fearing for the body, as it is definitely going to get destroyed. No need to fear for their being, as it is indestructible. As I am supreme being, I have no destruction. It is the same for you and everyone else as well:
"nityō nityānāṁ cētanaścētanānām ēkō bahūnāṁ yō vidadhāti kāmān" ॥ ityādiśrutēḥ।
"He is eternal among the everlasting entities. He is the sentient among the sentients. He is one among many. He grants everyone’s desires"–So states Vedas
"svadēhayōgavigamau nāma janmamr̥tī purā । iṣyētē hyēva jīvasya muktērna tu harēḥ kvacit" ॥ iti skāndē।
"The being obtains a causal body and experiences birth and death in the form of union and disunion with its body till its liberation. But never for Hari (God)."–states Skanda Purana
īśvarasyāpi yuddhagatatvānmōhāt tasyāpyubhayavidhānityatvaśaṅkāprāptau tadapi nivāryatē na tvēvāhamiti।
Even though Krishna is Lord, because of delusion, if someone doubts eternality in Him of either body or self, it is clarified by stating 'natvevaham' i.e., "never was there a time when I did not exist".
yadyapyēṣā śaṅkārjunasya nāsti। tathāpi prāptalōkōpakārārthaṁ bhagavatā nivāryatē। ēkāntē kathayannapi vyāsarūpēṇa tadēva lōkē prakāśayiṣyati hi ॥12 ॥
These doubts are not with Arjuna. Even then the lord clarifies for the sake of benefiting the world. Even though this episode happened only between Arjuna and Krishna, Vyasa published it in the world.
