Grief is described here as a kind of architecture. Mourning arrives with "all the small doors / that nobody might pass," a picture of countless little openings that no one can actually walk through. The speaker then turns inward: "a sad house am I." Grief isn't just something happening to them; they have become the building, full of closed or unusable entrances.
The middle of the poem shifts to anger and frustration. The speaker wishes death would "erupt," meaning it would be loud, dramatic, and large enough to match the feeling of loss, instead of simply returning us "to nothing." That quiet emptiness seems almost insulting.
The last lines ask whether "not knowing" is really the best way to live with all this. The mood is bare and unsettled. The speaker offers no comfort or answer, only a question left hanging, and the short lines and spare wording make the silence around it feel even larger.