Krishna describes the cosmic rhythm of creation and dissolution. When Brahma's day begins, all beings emerge from the unmanifest — like flowers opening at dawn. When Brahma's night falls, everything dissolves back into that same unmanifest source — like flowers closing at dusk.
A seed sprouts into a plant, the plant eventually withers and returns to the earth, and from that earth a new seed grows. The entire universe follows this same pattern — manifesting again and again, dissolving again and again.
This eternal cycle makes one thing clear: even Brahmaloka is not permanent, because creation and dissolution continue playing out there as well. Permanence exists only beyond this cycle — with God.