परस्तस्मात्तु भावोऽन्योऽव्यक्तोऽव्यक्तात्सनातनः | यः स सर्वेषु भूतेषु नश्यत्सु न विनश्यति || २० ||
paras tasmāt tu bhāvo 'nyo 'vyakto 'vyaktāt sanātanaḥ yaḥ sa sarveṣu bhūteṣu naśyatsu na vinaśyati
paraḥ—superior; tasmāt—to that; tu—but; bhāvaḥ—nature; anyaḥ—another; avyaktaḥ—unmanifest; avyaktāt—from the unmanifest; sanātanaḥ—eternal; yaḥ—which; saḥ—that; sarveṣu—in all; bhūteṣu—beings; naśyatsu—being annihilated; na—never; vinaśyati—is annihilated.
“But there is another unmanifest nature, eternal and beyond the cosmic unmanifest, which does not perish even when all beings perish.”
Here Krishna distinguishes between two 'unmanifests': the cosmic avyakta that is the potential state of matter before and after a cosmic cycle, and the supreme, eternal, sanātana avyakta that transcends even the cosmic cycle. The latter is Brahman—unchanging, unborn, undying, beyond all cycles of manifestation.
There is something in you that does not change when your moods change, when your body ages, when relationships end. It was present in childhood and is present now. Sit quietly and attempt to locate that which is always the same. That is the sanātana—the eternal that this verse points to.