Byron's poem is a satire of Robert Southey's A Vision of Judgment, which was written at the death of George III to celebrate his reign. Southey, the poet laureate, writes about George's triumphant ascension to heaven, where he is met by Saint Peter and other royal luminaries that predeceased him. Byron's take is very different. In his poem, St. Peter and the angels are bored from lack of work—George III's wars have driven so many into hell. When George arrives, Peter does not recognize him, because it seemed so unlikely that he would try to get into heaven. Satan arrives with George, and there is a kind of "trial" between Satan and the archangel Michael over George's fate in the afterlife. Numerous witnesses are called, including Southey himself, who is portrayed as a charlatan, offering to pen biographies of Satan and Michael, who both decline. When Southey begins reciting his poem, before he can get through the fifth line a kind of riot ensues, because angels and demons both are so desperate to get away. In all the commotion, George sneaks into heaven.
Byron's satire has several aims. First, he makes fun of the idea that George could get into heaven, given his warmongering and opposition to democracy. Second, he makes Southey a specific target, mocking his hypocrisy and condemning him for abandoning the liberal values he once held in order to be a kind of "shill" for George and the conservatives. Ironically, Southey's poem would be forgotten were it not for Byron's satire.