The poem begins with a simple warning: if you leave a space, the outside gets in. It could be a gap in a wall, a window, or a gap in a person's guard. The second stanza makes this feel more personal. Curtains that are left undrawn seem to stand for openness, but the poem doesn't treat that openness as freeing. The words are broken up and the syntax is hard to pin down, so "hope" and "ignorance" and "no plea" run together, as if the speaker can't quite finish a thought.
What comes through is a quiet unease that slides into regret. The futures that "coil / unwound" suggest plans that were never carried out, tightly wound and never released. The last word, "empty," lands flatly and leaves the poem hollow. The speaker seems to look back at a chance that was either missed or let in too carelessly. The mood is cold, spare and a little haunted, and the short lines and white space around them leave the reader feeling the same gap the poem describes.