द्वाविमौ पुरुषौ लोके क्षरश्चाक्षर एव च।क्षरः सर्वाणि भूतानि कूटस्थोऽक्षर उच्यते॥
dvāv imau puruṣau loke kṣaraś cākṣara eva cakṣaraḥ sarvāṇi bhūtāni kūṭa-stho ’kṣara ucyate
Word by word
The verse says
There are two beings in the world: the one that perishes and the one that does not. All creatures are the perishing one. The one that stands unshaken is called the imperishable.
In plain words
A piece of plain bookkeeping before the chapter's last move.
Kṣara - what wears out. That is every creature, every body, everything with a date on it.
Akṣara - what does not wear out. The unchanging layer underneath. Both are real. Neither one is the whole story.
Where you've felt this · at work
A workshop near you has been repairing cycles for forty years. Not one part of it is original. New shutters, new tools, the son at the bench instead of the father, a different wall since the road was widened. Everything you can point at has been replaced at least once. People still send their children there and say it is the same place.
Going deeper
Two columns are being set up so that a third thing can break them, and getting the setup right is worth a minute.
Kṣara means perishing. Everything with a body goes in that column - not as an insult, just as a fact about how bodies work. Akṣara means not-perishing, and it names the layer that never gets used up.
Almost every serious philosophy settles somewhere in these two columns. Either only matter is real and the unchanging is a story we tell ourselves, or only the unchanging is real and the world is a mirage. Both are tidy. Both leave you with half of your actual experience to explain away.
So the useful thing is not to settle yet. The temptation here is to decide that the real you is the eternal part and the perishing part can be written off - your body, your work, the people who will not last. That conclusion is cheap, and it costs you the life you are actually in.