Well... lots of symbolism. Hell, you're punished symbolically for the sins you commit on Earth. He mixes some paganism with Roman Catholicism, thus adding paganism to Roman Catholicism even more so. Outside of that, a good chunk of this book is Aligheri criticizing his political enemies and rivals. He spends more writing on Circle 8 (various forms of Fraud and Deception) as opposed to Circle 9, which is freaking TREASON of some form.
I think I wrote that institutional religion is failing today because those who run these institutions cannot connect with cultures that have evolved with templates of who and who is not a hero, good vs. evil, etc. despite their religions generally providing these templates because they fail to adequately use them. This is a fairly good example. The beginning is wonderful... but then it degenerates into the author attacking his political rivals for the most part.