The speaker keeps losing things, and each loss turns out to be a gain. First the hat is gone, and the reason given is oddly cheerful: now there is nothing between the head and the sky, so the speaker can see "more night." Then the room itself is "pulled down," as if the walls were just another cover to remove. Both losses are framed as choices, or at least as welcome trades.
The last stanza steps back and states the idea outright: art "cannot wait / upon hat or lodging." In other words, making art can't be put off until life is comfortable or sheltered. The title, "Minimalist," fits, since the speaker strips away possessions and shelter until only the night and the act of looking remain.
The mood is spare, quiet and a little defiant. There is a hint of humor in the tone, but also a real sense of wonder, as though being exposed to the dark is the price, and the reward, of paying attention.