The speaker of this riddle is a bookmark, though the poem never says so outright. It describes itself as a "slender leaf among leaves" that divides what has been read from what hasn't, and it keeps its place like a rest in a piece of music, guarding silence. The white field around it is the page, and the crows of forgetfulness are white too, so forgetting looks just like a blank page.
The bookmark marks where the mind, the lips, and the eyes stopped. It claims its shape doesn't matter, as long as it is flat and sturdy, "as the hope of continuance," the hope that we'll come back. The reader meets it only "under the covers," in bed, then sets it aside.
The mood is quiet, playful, and a little wistful. The speaker is humble, calling itself a "crutch" and listing the paperclips and receipts it might once have been, yet it takes its small job seriously. The closing "Riddle me" invites us to guess.