The Dante Symphony guides us through the Hell and Purgatory, but not Heaven. I think that this forces listeners to think about the idea of Heaven rather than have it be presented to them. Relating to Forms, Heaven is impossible for humans to accurately portray in any medium, be it speech, painting, music, etc. Liszt does, however, give the listener a taste of paradise at the end with the Magnificat. It is the only choral segment of the entire piece, and Liszt gave very specific instructions on hiding the choir from the audience's view to portray an angelic presence. Initially, Liszt had made the Magnificat even flashier than it already is to appease his mistress (she was a princess); however, his level-headed friend, Richard Wagner (should ring a bell or two... or three), talked some sense into him, telling him that the flashiness misrepresented Heaven. Now, on to the symphony itself:
The symphony begins in lento with Liszt's portrayal of the Gates of Hell (0:00-0:35 in the video below). This introduction, along with much of the symphony, is written in D minor, which key Liszt, quite appropriately, associates with Death (please listen to Liszt's Totentanz, written also in D minor, it's a personal favorite of mine and is very suiting for Halloween. Further, the Dante Symphony includes a large amount of tonal ambiguity, unlike pieces such as Totentanz. This deviation seems to contribute to treachery of Hell.
Soon--and indeed at varying times throughout the entirety of the Hell portion--the tempo accelerates, referencing the mounting terror and gravity of sin as Dante and Vergil descend. To demarcate the circles of Hell, Liszt uses a pronounced descent motif whenever Dante and Vergil are going deeper into Hell.
When they reach the Second Circle (that of the lustful), Dante encounters Francesa da Rimini just a he does in the Inferno. To convey the image of the tempestuous winds that Dante describes, Liszt uses rapidly ascending and descending chromatic scales. Tchaikovsky mirrored this technique in his Francesca.
Finally, the symphony is written in two movements (one of Hell, one of Purgatory) of ternary form. In ternary form, the composer introduces one segment, introduces a second one, and then returns to the (often augmented) first segment (called a recapitulation). This ABA structure mirrors the primary structure of the tercets in which Dante wrote his Comedy (aba bcb cdc ... rhyme scheme) and, by consequence, references the Trinity.
Alright, no more rambling: here's Franz Liszt's Dante Symphony as performed by the Berlin Philharmonic Orchestra under the conducting of Daniel Barenboim. Enjoy!