Gita : Ch-8. Slo-20.

Srimad Bhagavad-Gita :

Chapter-8. ( Akshara-brahma-yogam )

Slokam- 20. (  Yet there is another nature, which is eternal and is transcendental to this manifested and unmanifested matter. It is supreme and is never annihilated. When all in this world is annihilated, that part remains as it is.)

parastasmatu     bhavonyah     avyaktovyaktat     sanatanah,

yah    sa     sarveshu     bhuteshu      nasyatsu     na     vinasyati.

tu   =   but;

tasmat   avyaktat    anyah    =    from   that   unmanifest    another;

parah    sanatanah   =    transcendental;   and   eternal;

yah    avyaktah    bhavah    =   that,   unmanifest   nature;

sa     sarveshu     bhuteshu      nasyatsu   =   that    even    when    all   the   manifestations   being    annihilated;

na    vinasyati   =   never   annihilated.

The ultimate substance of the form of the atma is completely distinct from prakriti or the material substrtatum pervading existence and is without birth and death.
Thus it better then even the Cosmic Egg from where if one surmounts it there is also no return to material existence.

This Lord Krishna is indicating in this verse and the next by the words paras tasmat meaning superior to that.

His state is superior because He is totally separate from avyakta the unmanifest that emantes from Brahma and is invariably connected to prakriti or the material substratum pervading physical existence and the cause of the myriad of multitudes of variegated created beings alluded to in the previous verse.

Yet Lord Krishna is revealing that there is another superior avyakta which is different, being eternal and full of consciousness which never perishes and is imperceptible by any means and measure of proof except by the evidence revealed in the Vedic scriptures.

This superior avyakta coming from Him is never subject to destruction even when all the worlds and universes along with all movable and immovable beings are destroyed.

After completing the expose on the impermanence of all material worlds, Lord Krishna elucidates in this verse and the next on the eternal nature of the spiritual worlds which exist beyond avyakta the unmanifest and which is never destroyed when all the material worlds perish.

Beyond the avyakta is another superior nature, unmanifest which is the cause of prakriti, the material substratum pervading existence, and which exists as the cause of all things in the moving and non-moving universes.

This superior unmanifest is beyond the perception of the senses and without a beginning and it never ceases to exist even when all the worlds and all created beings, which are merely causes and effects, inevitably perish.

To be continued .....