In his introduction to Dante’s Inferno, Lino Pertile, an Italian linguist and Professor of Romance Languages and Literature at Harvard University, writes:
What is deeply disturbing for the modern reader is the endlessness of the state of being in which victims and tormentors are caught by the eye of the passing visitor: the notion that “great hailstones, filthy water, and snow” will never cease to teem over the gluttons’ naked bodies; that the Harpies will forever bite and feed on the leaves that clothe the limbs of the suicides; that a drop of water will never fall upon the parched lips of the counterfeiters; that, in sum, in the kingdom of death no one will ever be allowed not to live on and suffer. As he runs through the woods of the suicides desperately trying to escape the fangs of the ravenous hounds that pursue him, the squanderer Lano da Siena implores: “Now hurry, hurry, death!” In Hell, existence itself is the most implacable punishment. Faced with the “reality” of never-ending punishments, the reader is dismayed at the thought of a justice that can never be satisfied. The text does indeed compel us to react and respond to its provocations. The reasons for this are at least two, and both have to do with Dante’s extraordinarily original conception and consummate art.
First, outdoing all the visionaries and preachers of his time by leaps and bounds, Dante portrays not sins, but sinners. He gives form to a Hell in which theological and ethical principles, abstract and inaccessible to the many, are embodied in, and totally absorbed by, the stories of concrete men and women, for the most part Florentines or Tuscans — not necessarily “great” individuals, but certainly “true,” and known at least by name to his readers. A Hell where, even while sharing a common destiny, each character represents a specific sin, without however forfeiting any part of his or her own unique personal story, his or her own irrepressible individuality. All of the characters of the Inferno are defeated individuals, but each one is vanquished in his or her own unique way. The penal conditions to which they are subjected, the unchangeable form of their new existence, instead of dulling or extinguishing their individuality, illuminates it with unanticipated sparks and unsuspected complexity. Thus Dante reveals the actions of his friends and his enemies alike, he gives a voice to their thoughts; they in turn are given access to understanding life in a way they were unable to while living it.
In the second place, Dante does not limit himself merely to cataloguing sinners according to their crimes, but rather he explores human actions in their most secret motivations. A most original and compelling trait of Dante’s Hell is the notion that, while being all equally damned, the souls of the sinners are not all entirely nor equally reprehensible. Next to the perfectly “evil” figures (for example, Filippo Argenti or Vanni Fucci or Pope Boniface VIII), there are others in whom evil presents itself as a tragic flaw that either sudden death has rendered fatal or no virtue has been capable of conquering or compensating for: this is the case, for example, of Francesca da Rimini, Pier della Vigna, and Brunetto Latini.
But Dante does not stop here. His Inferno also shows that, if good people can lose their way forever, the “bad” can have positive characteristics that, while not saving them, nevertheless render their identity more rich and complex. . . . This is why the feelings of Dante the character towards the “lost souls” are not always and exclusively negative. As he descends deeper into Hell, Dante’s reactions range from compassion to aggression, from respect to contempt, from curiosity to revulsion, from pity to pitilessness. He swoons at the tale of Francesca’s fatal desire but, wilfully or by accident, he kicks Bocca degli Abati in the face; he delights at the torments inflicted on Filippo Argenti and Vanni Fucci, but feels filial affection for the disfigured Brunetto Latini. Before Farinata he in awe, and spellbound before Ulysses. Dante’s journey through Hell is a discovery of how deeply intertwined good and evil can be, in ourselves and as well as in others, and how difficult and painful it is for any human being to reach, without proper guidance, any kind of moral clarity.
Dante does not flinch from putting himself in God’s place as judge, nor does he question what he sees as God’s judgments; nevertheless, this sternness does not prevent him from feeling pity and involving his readers in his sorrow. The message is definitely mixed, but the lack of moral clarity on the part of the frightened, confused, and uncertain pilgrim is part of a strategy designed to affirm the absolute necessity of such clarity for the pilgrim’s (and our own) ultimate salvation.
— The Cambridge Companion to Dante, edited by Rachel Jacoff