Paradise Canto XVII: (Fifth Heaven, Sphere of Mars)
Something has been bothering Dante for some time and he wants to get it off his chest, but he cannot do so without first comparing his angst to some Classical character. This time, he calls himself Phaethon (the son of the sun god who got his wish of driving his father's chariot and crashed it into the desert), coming to talk to his mother about his wish.
Beatrice, reading Dante's mind, tells him to "show his desire" to Cacciaguida so that he can answer to his troubles. Beatrice makes it clear that both she and Cacciaguida already know both Dante's question and the answer.
Dante voices his concern: Cacciaguida, since you've made it into a Heaven this high, you have a good vantage point over all of time. When I was traveling with Virgil through Hell and Purgatory, he mentioned that my destiny would be difficult. I want to know what those hard times will be, so I can mentally prepare myself for dealing with them.
Cacciaguida responds kindly—not with the usually vague and mysterious words of prophecy, but with plain simple words like those Christ used for his followers.
He tries to comfort Dante by telling him about contingency. This is the principle stating that even though something has been foretold, it does not mean that it will necessarily happen; in other words, God doesn't make it happen.
Dante, just like Hippolytus of Athens, will be forced into exile from Florence. He will leave everything he loves most dearly and will have to serve others. What will be hardest for Dante to bear is that his fellow exiles will be "insane, completely / ungrateful and profane" against him, so that Dante would do best to bear this tough time alone.
He will find some friends, though: a great Lombard (Bartolemmeo dello Scala), who will house him, and Bartolemmeo's younger brother, Cangrande, who will be a major military force. He will gain a reputation for "hard labor and… disregard for silver" and will be a hallmark of generosity and honor.
Cacciaguida assures him, saying, "your life will long outlast the punishment / that is to fall upon their treacheries," meaning—of course—that Dante will earn salvation.
This encourages Dante, who declares himself prepared for the hard times ahead. He promises to hold his course steady by continuing to write poetry.
Dante, reflecting on his journey so far, knows that for many people it would've been too difficult. Seeing the truth is always difficult, but Dante vows to not be "a timid friend of truth."
Cacciaguida encourages him by saying that even if people today consider Dante's honest words too harsh, they will—after mulling over them—find them just and correct. And Dante will win honor for daring to speak truth against the highest and most corrupt powers.