At the coming of Day, all manifest forms spring forth from the unmanifest; at the coming of Night, they dissolve back into that very same thing, called the unmanifest.
Explanation
Krishna continues describing the cosmic day and night of Brahma (the creator), introduced in the previous verse. When Brahma's day begins, the visible world emerges from the unmanifest (avyakta), the unseen source; when his night begins, it dissolves back into it. Traditions differ on what the unmanifest here is: some take it as primordial nature (prakṛti), others as Brahma's own unmanifest state.