B.G 2.20
न जायते म्रियते वा कदाचिन् नायं भूत्वा भविता वा न भूयः । अजो नित्यः शाश्वतोऽयं पुराणो न हन्यते हन्यमाने शरीरे ॥ २-२०॥
na jāyatē mriyatē vā kadācin nāyaṁ bhūtvā bhavitā vā na bhūyaḥ । ajō nityaḥ śāśvatō’yaṁ purāṇō na hanyatē hanyamānē śarīrē ॥ 2-20॥
The Lord is neither born nor does he die. The ever existent neither come into being nor ceases to exist. The Jīva transmigrating from one body to another is unborn, eternal, and permanent (as he is similar to Lord). The Jīva is not destroyed when his body is destroyed.
Gīta Bhāshya 2.20
Lord is eternal and the same always. Jīva is eternal, as he is similar to the Lord. But, he has a variance in knowledge, unlike the Lord. As Jīva travels from one body to another, he is called ‘purāna’.
Even the Vedic hymns accept that the being is unborn. But unlike the knowledge of the Lord, knowledge of the being undergoes variations. It is so stated in ‘tadaikshata’ Vedic statement (chāṁ.u.6.2.3).
“In all places and time, in all states, without there being a difference in its nature or form, Lord with his knowledge is the same.” - bhāga.3.7.5
So he is famous in Vēdas and Purānas.
How is Jīva eternal? Because of its similarity with eternality and other qualities of the Lord. Eternally Lord has a single unchanging form. Jīva is called 'purāna' as he travels from one 'pura', body, to the other. Therefore, even when the body is destroyed, it does not cease to exist.
