A worker arrives before dawn at what appears to be a store, pushing a cart, and feels the whole place is barely real. The lights flicker on only partly, and the speaker imagines them forming a ceiling that shuts out the sky. The repeated word "uniform" does double duty: the lights are uniform, and so is the speaker, both "not exactly awake."
The tone shifts in the middle. The speaker imagines that the economic system took a heavy blow overnight, yet will still get back up because workers like them keep hauling themselves up too. There's a tired, wry recognition here: the system survives only because people dream its stores, factories and warehouses into being each morning.
The ending is quiet and small. The first customer, an old man in big headphones, is only "probably" coming. After the big claims, the poem settles on one ordinary person, which makes the mood feel groggy, resigned, and oddly tender.