। ॥ ५८८ ॥
In plain words
The Upanishads declare that in deep sleep and similar states, the universe assumes an unmanifest condition. Therefore, scripture designates that subtle state of distinction simply as the unmanifest.
Close to the Sanskrit
The scripture speaks of the state of the world as being of an unmanifest nature in deep sleep and other states; therefore that distinction is the unmanifest, thus [says] that [scripture].