Hatred is where this sonnet begins, and by the last line the speaker admits it was aimed too narrowly. He calls himself a republican, and he opens with a flat confession in the past tense: "I hated thee, fallen tyrant!" The first eight lines justify that hatred. Then a bitter "I know / Too late" swings the poem toward a bigger target. The real enemy is not Napoleon but whatever outlasts any single ruler.
The charge against Bonaparte is that he wasted a chance. Calling him "a most unambitious slave" is a deliberate paradox, since a man who seized an empire is condemned for thinking small. He might have built a throne that lasted, "Where it had stood even now", but he "didst prefer / A frail and bloody pomp". The line break after "prefer" makes the choice hang in the air. "Pomp" is a deflating word that suggests ceremony and glitter with nothing behind it. The image of him "dance and revel on the grave / Of Liberty" turns his rule into a party held over a corpse. Time then sweeps his achievements "In fragments towards Oblivion", like debris on a floor.
The middle of the poem is a strange, almost vengeful prayer. Shelley lines up capitalised abstractions (Massacre, Treason, Slavery, Rapine, Fear, Lust) as if they were assassins. The speaker wanted them to "creep" on Napoleon's "sleep" and smother him. The verb is intimate and stealthy, more like a nightmare than a battlefield. The final phrase of the passage, "their minister", carries the joke. These vices were not his enemies but his servants. The speaker had prayed for tyranny's own agents to turn on their master.
The form helps to show a mind changing direction. The rhyme scheme runs abba cdcd efef gg. It is neither a strict Petrarchan sonnet nor a Shakespearean one but a hybrid of the two. The enclosed opening rhymes ("groan" and "throne") close around the speaker's anger like a fist. The alternating rhymes that follow loosen the pattern, and the couplet snaps shut with a verdict. The metre is a fairly regular iambic pentameter, but the sentences keep cutting across the lines. In line 7 a full stop falls in the middle ("Oblivion. Massacre,"), and the word "Massacre" is dropped at the line's end like a blow. Because "Too late" is carried over a line break, the regret seems to arrive a beat after the knowledge. Napoleon and France, we are told, "are in the dust" together. The poem does not name what comes next, but the phrasing hints that the tyrant's fall is no clean victory for the people.
The couplet delivers the poem's central idea. Virtue's "more eternal foe" is not "Force or Fraud", the very crimes of a Napoleon, but "old Custom, legal Crime, / And bloody Faith". "Legal Crime" is a sharp oxymoron, because it names wrong that has been made respectable by law. "Old" and "eternal" set these enemies against the "frail" tyrant, who lasted only briefly. The poem does not say what "Faith" means. Established religion is a plausible reading, but that is an inference. What the text does show is the echo of "bloody": Napoleon's "bloody pomp" and the "bloody Faith" are linked by a single adjective, as if they were relatives.
The last line adds a final irony. "Time" appeared earlier as the force that sweeps Napoleon's pomp away, which suggests justice. Now Time is the parent of "the foulest birth". The same process that destroys a tyrant also breeds the habits that tyranny feeds on, and the rhyme of "Crime" with "Time" locks the two together.
The poem is significant because it refuses an easy celebration. A political sonnet might be expected to cheer a tyrant's defeat, but this one turns on its own hatred and treats it as a kind of misjudgment. In fourteen lines Shelley moves from personal anger to political analysis and ends with a darker claim: that deeply rooted, respectable institutions can threaten freedom more durably than any single despot.