The title suggests a used book, and the poem begins with what time has done to it: a patch of mould spreading across the pages, shaped like a round, abstract letter "o." The mould looks almost like writing, as if decay has added its own handwriting over the printed words.
Then the speaker steps in. They are scraping the mould away, and they call what they remove "such glory." That phrase is the surprise. Cleaning off damage is a practical, even tedious job, yet the speaker seems to feel they are destroying something beautiful. The poem doesn't say so outright, but the word "glory" hints at a mix of admiration and regret.
The mood is quiet and a little uneasy. In just a few lines it captures a small tension: caring for a book means erasing a mark that is, in its own odd way, lovely. The speaker is caught between repair and loss.