So I got through "The Divine Comedy" (and the Cliffs Notes because that shit was hard yo). Here are some of my thoughts.
"Inferno" is the most popular because it's vivid. All that torture and gruesomeness, all those spiteful wretches cursing God and each other for sins such as charging interest (take that, capitalist pigdog!). The geography of Dante's hell as a giant pit, unnaturally divided into a series of concentric circles, with rivers of blood, water, and fire flowing down to the ice where Satan is frozen in the center of the earth. Cool.
Once Dante and Virgil crawl past Satan through the earth's core, they flip upside down, because every medieval scholar who read from antiquity knew the earth was round. We're just taught it was Columbus's idea because someone, probably during the Enlightenment or neo-Classical period, realized that it made a good story.
Next is "Purgatorio," which might be my favorite. Purifications in purgatory mirror punishments in hell, and the sins are basically the same. So we can face mistakes, wrongdoing, tragedy, and failure like those in hell by cursing the world and doing more wrong. Or we can be like those in purgatory, who see the hardships dealt to us by the cosmos as chances for growth.
One of the only (if not THE only) time Jesus describes heaven and hell is to describe them as exactly the same: a giant feast in which everyone's arms are too short and their silverware is too long for them to feed themselves. Everyone in hell is angry and hungry, whereas everyone in heaven is happy because they're feeding each other. Fittingly, purgatory is the reverse shape of hell; instead of a series of concentric pits, it's a mountain of concentric higher slopes, as if it were the earth pulled out of the ground in order to make hell.
"Purgatorio" is also the most dramatic. Aside from Dante himself, no one in hell or heaven is going anywhere. But souls in purgatory are on the move. My favorite character is a pope in purgatory who, for most of his life, was a total douchebag, living for power and money, and made it all the way to the papacy. Only in the last months of his life, when he was the most powerful man in the world, did he realize the emptiness of his pursuits and change his ways.
Speaking of drama and movement, Dante (the character in the Comedy, separate from the poet) has a story of his own, thin though it might be, stretched across the 100 cantos. It would be inaccurate to call the Comedy "the story of Dante's redemption," but it's still there. He's not just our eyes and ears. If one were to adapt the Comedy for film (some kind of 3 - 6 hour special effects extravaganza, but still a film), one would probably make Dante's story into a stronger throughline.
Anyway, Beatrice, a girl he fell in love with when they were about 9 but never really got to know before she died young, has sent dead Greek poet Virgil to take Dante on a trip through the afterworld. She's done this because he's lost his way in middle-age. Whatever bad thing(s) Dante did to warrant a trip through heaven and hell is never specified; it's suggested that he's just caught up in the mundane, with no thought for anything else. Beatrice's death did not cause him to sin.
It's like he's going to work, coming home and watching TV, day after day, with no thought for his personal growth or eternity, when suddenly a poet's ghost shows up and says a dead girl he hasn't seen since grade school needs him to change his ways. And then when Dante finally meets Beatrice in the Garden of Eden at the top of purgatory, and he's all happy to see her again, the first thing she does is bust his balls for losing his way.
The Garden of Eden is where we say good-bye to pre-Christian Virgil, who represents pure reason. We don't say "good-bye" so much as he vanishes into thin air while Dante is getting chewed out by Beatrice. Beatrice can never be as fun as Virgil because, while she protects Dante from afar while he's in hell, Virgil is an active and visibly caring protector, even fatherly.
And Virgil is tragic: after a trip to purgatory, it's back to hell for him. He must return to being a himbo in Limbo. Dante's solution to the problem of how a just God could condemn just pagans to an eternity in hell is by making Limbo - the afterlife for well-behaved non-Christians - not a bad place at all, free of torture, where benevolent Hindus and atheists presumably chill for all eternity, smoking fatties.
Virgil goes away because, despite Dante's and the medieval Roman Church's fascination with reason, reason alone cannot save you. In paradise he is quizzed by 3 apostles, not so much on reason, but on faith, hope, and charity. (As an aside, this is more in line with the more mystic-centric Orthodox Church's means of salvation. Russian iconographer Andrei Rublev, in my userpic, was born about 30 years after Dante died, and would not have been nearly so interested in Virgil and reason).
I'm a firm believer in the limits of reason. It's great for comprehending the physics of the physical universe (mysticism may get you to nirvana, but it can't get you to the moon). But I don't think you can derive capital-M Meaning from reason, and you certainly can't understand people and human desires using it. People want what they want and come up with "reasons" later, even if it's a split second later and they don't even realize it. Anyone who claims he's being "reasonable" is a liar or mistaken.
Stanley Kubrick would back me up on this. In "2001: A Space Odyssey," the perfectly reasonable machine-people of the future are in as much of a repetitive rut as the pre-tool apes. The perfectly reasonable HAL 9000 and the spaceship Discovery (shaped like a human nervous system, natch) can only go so far. Only Bowman's finally intuitive, "mystical" leap allows him to evolve.
But just as John Paul II referred to the mysticism of the Eastern Orthodox and the intellectualism of the Latin West as "the Church breathing with her two lungs," so too Dante sees both the active and contemplative mindsets as necessary for the full human experience. Old Testament figures Leah and Rachel embody the active and the contemplative in the Earthly Paradise (although I forget which is which). Since Dante himself is more active than contemplative - devouring ancient scholars, going on and on about politics - it's big of him to rate contemplation and mysticism so highly. Hilariously, monks are in one of the highest heavens, while "fallen nuns" get a lower paradise.
But I digress. Anyway, Virgil is replaced by Beatrice and we enter "Paradiso," the driest and least-read of all the Comedy. Even the Cliffs Notes break down at one point and refer to Beatrice's answer to one of Dante's many questions as "long, complicated, and typically medieval." With no juicy torture, sins, or progress to be made, "Paradiso" is nice people being happy. Drama is sucky people making bad choices and suffering until they realize they error of their ways, become happy for about 45 seconds, and then the story ends. "Paradiso" is probably the longest post-denouement ever written.
Paradise is divided into several heavens, where some souls get to be closer to God than others (or not - it's a little unclear - they might exist in their separate heavens and within God at the exact same time). Even this doesn't bother the souls of the saved because they've learned to accept and find joy in the order of the universe. The hierarchical, ordered structure of paradises mirrors the medieval perception of the hierarchical, ordered structure of the entire cosmos.
The downside to this philosophy is that it can be used by the powerful to keep the peasants / proletariat in place. It can also be used by the lazy to say "I can't change the world, so I might as well just sit around watching TV all day." Still, what's that bit from the Al-Anon prayer, the one often attributed to St. Francis? "Give me the strength to change what I can change and accept what I cannot"? We should "covet righteousness," we are to seek growth and change and improvement, yet philosophically accept setback and even failure, to accept that this moment is not "the fullness of time." And not to yell at traffic.
The ever-active Dante would probably agree with this: his constant heckling of monarchs and popes alike, and his high hopes for new leaders to balance the powers of church and state, hardly suggests stupefied complacency and acceptance of the status quo.
So that's what I got out of "The Divine Comedy."