The speaker is writing about a friend, Helen, whose name brings them comfort the way moonlight does in a dark night. The moon runs through the whole piece as a metaphor: she is bright and colourful, but, like the moon, she has a side she never shows. The speaker describes her as a kind, young soul living in a world that seems to want her to be hateful, a "rebellious, trembling mess of stars" who still makes flowers grow from ruins.
The feeling underneath is admiration mixed with worry and longing. The speaker sees how much she gives up for other people's happiness and safety, and wishes she would come back, which suggests she is absent or out of reach. The closing questions, asking if she is a star, stardust or the moon, show the speaker trying to understand someone they only partly see. The mood is tender, wistful and a little sad, though the last line leaves a hopeful hint that she may still be keeping them company in the dark.