The entire content of this mail is from Swami Chidbhavananda's translation of The Bhagavad Gita, & Swami Adidevananda's translation of Ramanuja's Gita Bhashya, both published by Ramakrishna Mission
Immortality 20-22
1 Gita Sloka every day - Chapter 8 - Akshara Brahma Yoga - Sloka 20
Parah tasmat tu bhavah anyah avyaktah avyaktat anatanah I
Yah sah sarveshu bhuteshu nashyastu na vinashyati II sloka 20
परः तस्मात तु भावः अन्यः अव्यक्तः अव्यक्तात सनातनः
यः सः सर्वेषु भूतेषु नश्यत्सु न विनश्यति I I श्लोक 20
There is however, another unmanifest being than this non-manifest entity, which is eternal; this is not destroyed when all the entities are destroyed.
1 Gita Sloka every day - Chapter 8 - Akshara Brahma Yoga - Sloka 21
Avyaktah aksharah iti uchatah tam ahuh paramam gatim I
Yam prapya na nivartante tad dhama paramam mama II sloka 21
अव्यक्तः अक्षरः इति उच्तः तं आहुः परमां गतिं I
यं प्राप्य न निवर्तन्ते तद धाम परमं मम I I श्लोक 21
This has been called unmanifest (Avyakta) and Impersihable (akshara). This they say is the highest goal. This is my highest abode, reaching which the selves do not return to samsara.
Brahman is this unmanifested reality. It is designated in this way because It is incomprehensible and inaccessible to the mind, intellect and senses. It is further designated as the Imperishable because of its being ever constant undergoing no modification whatsoever.
Prakriti is also called unmanifested when it is in pralaya or dissolution. It is then inaccessible to the mind, intellect and senses. But the difference between the two has to be borne in mind. Prakriti is ksharam, perishable while Brahman is aksharam, Imperishable. Beings involved in Prakriti continue to appear and disappear; beings that attain Brahman do not undergo these changes. They do not return. Brahman beig the highest and constant abode for beings, it is called teh Lord's supreme abode.
The way to attain this abode is given in the next sloka