Canto VIII is weak in construction. Too much happens: A signal is given, a boat appears, Virgil has a short argument with the boatman, Dante has a fierce argument with Filippo Argenti, and so on. Why Argenti is singled out for mention remains an enigma, but apparently, he was a bitter enemy of Dante's and reveals himself as a man marked by all the passions, hatreds, and loves of his time. Prior to Canto VIII, there was one circle chiefly described per canto; from this point onward, however, circles overlap, and Dante the Poet devotes multiple cantos to single circles.
The theme of politics also shows up in Canto VIII. In fact, the most important action in this canto is the altercation between Dante and the shade of Filippo Argenti. Argenti was a bitter enemy to Dante, and his family opposed Dante's return to Florence.
Dante's character is indeed changing, as his reaction to Argenti (wishing him to suffer beyond what he already suffers among the throng of Wrathful) shows this change. By wishing Argenti more harm, Dante behaves wrathfully, just as the sinners in the marsh behave. Nevertheless, Virgil praises Dante highly for this behavior. Dante no longer feels pity for the sinners.
Dante and Virgil move on toward the City of Dis, the capital city of Hell, where the sins of violence and heresy are contained. The mythological king of the Underworld (Pluto) is sometimes called Dis, thus this city is named for him.
Once at the gate to Dis, the damned souls are angered at Dante's presence, and they refuse him entry, saying that Virgil can come in, but only to stay. In this encounter, Virgil is unable to convince the shades to let Dante through. Allegorically, this trouble shows that even human reason and wisdom cannot overcome every obstacle and that divine intervention is far more powerful than anything a human offers.
