The speaker begins with a calm, almost stubborn confidence: he believes plain words, and he is ready to die without fuss. But the poem quickly turns strange and violent. A hat is knocked off, and beside it sits a severed head "served up on a stick." The speaker insists he is better than that hat, as if refusing to be reduced to a symbol, even while the head seems to be his own or someone like him. The image suggests what happens to people who take sides.
Then the tone shifts. Someone is shouting about "the infinite," and the speaker admits how little anyone can truly know, even "any small plain thing." That makes his earlier readiness to believe look shakier. The ending is quietly honest. Sure of himself "as a drunk," he grieves for half an hour over the just demands of the poor. The mood is wry, uneasy, and self-mocking: he sees that his conviction is real but short-lived, and he doesn't let himself off the hook.