Why does Dante go on this journey?

Dante, Inferno, Books 1-5, 11

Questions for Discussion Post, due 6-12, 

1. Why does Dante go on this journey? (which, besides hell/inferno, also encompasses the purgatory and paradise/heaven)
2. What sense of divine justice, as well as the direction of his own life, does D./the traveler receive?
   1. How is justice done? In other words, who receives what punishment for what deeds/sins/transgressions? Why are the sins/transgressions ranked according to these levels?  Which are the lightest, which are the worst?
   2. What do you think of the concept of “contrapasso” or counter-penalty?
3. Do all suffer/get punished equally?  Why do some suffer more than others? In other words, is the system of divine punishment (from that you've read so far) just or unjust? Which sense of justice do you receive from this? Which sins or transgressions seem to be missing? Which are ranked or weighed too high or too low? Is anyone unjustly placed into hell?

4. What is the role of pity (both Dante/the speaker’s pity and our pity/the reader’s pity)?  Why does D. pity certain souls? Does pity imply the injustice of their punishment? Is there ever any doubt of God’s justice?