Sanskrit
परस्तस्मात्तु भावोऽन्योऽव्यक्तोऽव्यक्तात्सनातनः । यः स सर्वेषु भूतेषु नश्यत्सु न विनश्यति ॥
paras tasmāt tu bhāvo'nyo'vyakto'vyaktāt sanātanaḥ yaḥ sa sarveṣu bhūteṣu naśyatsu na vinaśyati
Translation
Therefore verily there existeth, higher than that unmanifested, another unmanifested, eternal, which in the destroying of all beings, is not destroyed.
Annie Besant · The Bhagavad-Gita, translated by Annie Besant (4th ed., 1922) — Wikisource · Public Domain
Explanation
The turn the chapter has been building toward: beyond the unmanifest of verses 18-19, the one bound up in the day/night cycle of manifestation and dissolution, there exists another unmanifest — eternal, and not destroyed when everything else is. This second, higher avyakta is what verse 21 will identify by name as akshara, closing the loop back to brahman’s definition in verse 3.