The title gives the key: "remorse" is regret, and here it belongs to a reader who feels sorry for having read. The poem is only a few lines long, but it packs in a sharp worry. Books are compared to ships, and each one carries "fresh stowaway selves" – new identities, voices, and ways of thinking that sneak aboard the reader without asking. Reading, the speaker suggests, doesn't leave you unchanged. You take in other people's styles and ideas until you're no longer sure which thoughts are yours.
The second part turns into a plea: "give me back / my plain words." The speaker sounds tired and a little desperate, wanting to return to a simpler, more honest way of speaking. The mood is wistful and uneasy, but also quietly funny, since the complaint comes from someone who clearly loves books. The short lines and bare wording make the request feel genuine, as if the speaker is already trying to speak plainly.