The poem begins like a monster story. A dragon-like beast with spinning eyes, flared nostrils and pin-sharp teeth prowls around your home, and it seems to retreat once you're safe. The imagery is vivid and a little childlike, the kind of danger we all learn to picture early on.
Then the speaker changes direction. Real evil, they say, isn't dark and cold, because if it were, spotting it would be easy and everyone would be "good as gold." Instead it wears an ordinary face, "like you or me," and can even seduce you, as in the pleasant image of the lemon tree. The ordinary setting makes the warning feel more unsettling.
The speaker sounds earnest and protective, almost like someone giving advice to a younger person. The mood starts out tense and fairy-tale spooky, turns uneasy and thoughtful, and ends on a hopeful note. Be strong, smart and kind, the speaker says, and together we'll defeat evil someday.