The speaker casts himself as a prophet nobody listens to, which is what the title, "Prophet without honor," suggests. His message is bleak: winter is coming, and life has a thorn in it. He isn't predicting anything exotic, just the hard, ordinary truth that cold and pain arrive for everyone.
Then the poem turns personal. A black flower goes to his Valentine, a gift that twists the usual romantic gesture into something dark. Yet the last line softens the gloom: "we were merry and broke." The past tense hints that this happy poverty is now a memory, so the poem may be looking back with some tenderness, or some loss. Judging by the tone, the speaker seems wry rather than despairing. He knows winter is coming, but he remembers being cheerful and penniless with someone he loved. The mood is cold and shadowed, with a small warm spot at the end.