Lost in a dark wood… (Inferno Cantos I-II)
Dante is at a major crossroads in his life. He is lost in a dark wood, allegory for deeply sunk into sin, and desperately in need of help. The three animals—the lion, leopard, and she-wolf—blocking his way to the sunlit hill represent Dante's unworthiness to reach Heaven just yet.
Virgil steps in and wins Dante's trust. He tells Dante that he has been sent by Beatrice, Dante's childhood flame, and ultimately by the Virgin Mary herself, who sees Dante's deep trouble and his need for a long, hard, educational journey through the Divine Realms, starting with Hell.
Hell is scary, but Purgatory is cool (Inferno III-XXXIV, Purgatorio I-XXVII)
In the passage through Hell, Dante struggles past frightening guardians and is almost torn apart by demons. In less scary moments of respite, Dante meets some old friends or sinners he sympathizes with, like Francesca, Brunetto Latini, and Ulysses. Through Virgil's stern lessons, Dante goes from sentimentalist to condemner and begins commiserating with Divine Justice.
In Purgatory, there are no monsters or thrilling escapes, but there are temptations—like Sordello's music, the siren in Dante's dream, and the forbidden fruit on the terrace of the Gluttonous. Dante recognizes his sin of pride and begins humbling himself by self-imposing the punishment of the Prideful. Upon meeting Statius, Dante knows him to be a masterful mentor and begins subjecting himself to his authority, instead of Virgil's.
Arrival and Frustration
Beatrice gives tough love. (Purgatorio Cantos XXVIII-XXXIII, Paradiso Cantos I-XXIII)
Upon arrival in the Earthly Paradise, Virgil disappears, much to Dante's distress. After Dante has lost his beloved mentor, Beatrice promptly begins to accuse him of horrible sins; sadly, her accusations are true. In her intimidating inquisitor mode, Beatrice asks Dante a series of questions about his morality after her death. Dante, humiliated, answers them in a scathing confession. Later, Beatrice entrusts him with his poetic mission.
The rest of this section, from Dante's purgation in the river Lethe to the journey through Paradiso, does not really fit into the conventional "Arrival and Frustration" stage because Dante doesn't directly go from his frustration to the final ordeals. There is a respite in between in which he has a fairly easy time of it in Paradiso, just absorbing information from Beatrice as he goes along.
The Final Ordeals
Got Faith? How about Hope? Charity too? (Paradiso Cantos XXIV-XXVI)
Dante undergoes a three-part oral examination by three of Christ's Apostles, St. Peter, St. James, and St. John. They test him on his theological knowledge of faith, hope, and charity. Each one makes sure that Dante knows the definition of the Theological Virtue in question, where it comes from, and that Dante has possession of it. Beatrice shows her support by helping Dante in the second test, so that he does not seem too proud.
St. John's examination is most nerve-wracking because Dante loses his sight, does the test blind, and is scolded frequently for not giving answers that are adequately specific. However, he passes all three exams and is rewarded by a blessing from each saint and approval to continue to the highest level of Heaven.
God… (Paradiso XXVII-XXXIII)
There are many parts to this reward. Dante gets to see how the angels do their work, he has his vision perfected and sees the Celestial Rose as it really is, he gets a tour of the Rose, a direct blessing from the Virgin Mary, and finally the worthiness to lay eyes on God himself.
The ramifications are mind-boggling. Not only does Dante pretty much get a guaranteed pass into heaven after his death, but he also knows what lies in store for him and a knowledge of the Divine Realms which he conveys in his superb poetry. To top it all off, he could potentially save others through his work. Talk about a legacy.