As a reader who comes from a Protestant background (with little or no exposure to the doctrine of purgatory), I came to this text with significantly less anticipation than I had for the Inferno. But Purgatorio may turn out to be my favourite book in the Divine Comedy. Here, the majority (I say "majority" because it is quite rare for souls to go straight to heaven) of heaven-bound souls ascend a multi-levelled mountain (which, like Hell, is broken up into levels based on each of the seven fatal sins) in order to purify and refine themselves from those sins that they could not surmount during their lives. Its important to bear in mind that, as with the Inferno, Dante's God is not some abstract judge who arbitrarily imposes the distinction between sin and salvation on humanity; rather, such categories are the product of human actions. These souls are in purgatory because they still feel the effects of their sins. In other words, sin is a real, material problem, and purgatory is a necessary passage for one on her way to paradise. Often portrayed popular culture as an uneventful nowhere-land, purgatory is actually the only location of the Divine Comedy in which all events happen in real time; or to put it a bit differently, time must pass for change to happen. All souls found in purgatory have been saved and have no cause for fear; it is hope that keeps them in ascent, it is hope that gives them momentum.
In good Aristotelian fashion, Dante construes human freedom as the right ordering of one's inner state (comprised of the intellect, the emotional appetites and the vegetative powers), which corresponds to the proper use/direction of desire. As Virgil explains to Dante,
"Neither Creator nor His creature, my dear son,Purgatorio can thus be characterized as the place in which human souls work out (and struggle through) their desires. Inferno, in contrast, is a tour of all the various ways humans are enslaved to their desires. The fires of refinement are not found in hell (where it is cold, windy and stagnant) but in purgatory.
was ever without love, whether natural
or of the mind," he began, "and this you know.
"The natural is always without error
but the other may err in its chosen goal
or through excessive or deficient vigor.
"While it is directed to the primal good,
knowing moderation in its lesser goals,
it cannot be the cause of wrongful pleasure.
"But when it bends to evil or pursues the good
with more or less concern than needed,
then the creature works against his Maker.
"From this you surely understand that love
must be the seed in you of every virtue
and of every deed that merits punishment." (XVII.91-105)
Again, Dante's theological and philosophical project resists the abstract character of modern thought. There is no gap between the reality of salvation and the experience Dante recounts; nor is there what now seems like an inevitable separation between reason, ethics, and faith from the competing desires that constitute human nature. Here, the human subject always functions as a desiring creature. Following Augustine, for Dante, it is not question of whether to desire or not (a point most pietists get wrong), but of how and what we desire.
In classical theology, desire is not a choice but an ontological condition: it is the very substance of our Being; and as such, Being is dynamic and diverse. Virgil tells Dante that "since no being can conceive of itself / as severed, self-existing, from its Author, / each creature is cut off from hating Him" (XVII.109-111). For me, these few lines from Dante do good job of summing up the "secular" mentality of Milton's Satan (i.e., "A mind not to be chang'd by Place or Time").