। ॥ १६ ॥
In plain words
Brahman alone is eternal; everything else, without exception, is not. That knowing — just that — is what is called nityānitya-vastu-viveka: telling apart what lasts from what passes.
Close to the Sanskrit
Brahman alone is eternal, but whatever is other is indeed non-eternal — such is the knowing. That very one is called nityānitya-vastu-viveka, the discrimination of eternal and non-eternal things.