Creation is from unmanifest to manifest, and go back again to unmanifest. It is a cycle which has no beginning - anādi, because there was no real creation (action or process of bringing something into existence). Since this cycle has no beginning and the same set of jīva is being recycled again and again, can we said that jīva is also ananta - endless? No, even though jīva has no beginning, but it has an end, other wise teaching of vedānta will be useless. Next Lord Krsna is going to explain this subject matter.
parastasmāttu bhāvo'nyoh avyakto'vyaktātsanātanah |
yah sa serves bhūtesu naśyatsu na vinaśyati ||8.20||
But distinct from that unmanifest is another unmanifest which is existent and eternal. That is not destroyed when all beings are destroyed.
When jīva drops his/her current physical body, jiva's subtle body together with causal body will travel to another body. This process has no ending, till the resolution of the world, subtle body of the jīva will also dissolve into the causal body. The causal body is in unmanifest form, which will spring out into the manifest again. As an individual jīva, one can cut off this cycle of samsara by removing the ignorance which is called causal body here. This ignorance in the individual level is the cause for individual subtle and physical body. In the total level, it is called māyā.
Lord Krsna wants us to understand the distinction between this unmanifest māyā and another unmanifest which is brahman, the very nature of the creation. This unmanifest māyā as the cause of everything that is manifest, is not the final cause after all, it is only another upādhi - limited condition. When an individual recognised his/her true nature which is brahman, individual ignorance is destroyed, there is no further subtle and physical body will be created, and what is left is existence eternal brahman alone. Therefore the causal body is also anitya - not eternal with reference to brahman. Therefore brahman is said to be parah - superior here.
Further, this final cause is being explained.
avyakto'ksara ityuktah tamāhuh paramām gatim |
yam prāpya na nivartante taddhāma paramam mama ||8.21||
The unmanifest was spoken of as not subject to destruction; they say that is he highest end gaining which they do not return. That abode of mine is the highest.
This true nature of mine is aksaram - not subject to change (including birth and destruction). It is the highest end, by gaining which there is no return. When anything is created like the world of deities, they are subject to time, therefore it will also end. And the meditator who gained it there, is also subject to return.
paramām gatim - highest reaching. To reach somewhere, travelling is required, but reaching in this path doesn't require any traveling. Because ātmā - my self is what I am gaining. For ignorance people who don't know one's self is limitless, living in the life of becoming, always reaching to be someone different, therefore the word gatim - reaching is used. The reaching here is not the reaching as understood by ignorance people, this highest reaching is not separated from oneself, so the seeker of moksa is not separated from moksa. Since the seeker and the sought are one and the same, the only reaching is by removal of ignorance.