Dante's journey through the 3 realms of the dead is told in a way that imitates or mimics the old epic poems. Those used to have great heroes, mythical creatures and active gods. All of that, though, was substituted by elements of the Christian Mythology; opening a lot of space for spiritual themes, demons, hell, angels and many other things that were used as substitutes by the often supernatural participants of old epic poems.
In, "The Divine Comedy," Dante wrote it to mirror a classic epic poem, but with Christian views. This means that he had to change just about everything that had to do with being Mythological. He had to some way replace the Muses with something else; he ends up calling to the Muses, and says what will happen if they actually do help. Virgil is his guide throughout most of the story, being his "mentor." Virgil helps Dante, the pilgrim to find his way to the Gates of Hell. Hell is another place where Dante reverts back to the old epic poems from Mythology: he places Charon, the boatkeeper, and the mythical creature, Minos, who judges their crimes/ sins and determines what their punishment should be. This is where the concept of "contropasso" comes into play: this means that the punishment of the sin either is the sin or is the mirror of that sin. Those who have not sinned, but did not get baptized, are sent to Limbo, where they cannot go to Heaven, but are not punished like those of Hell. All those who have not sinned and have been baptised, goes to heaven.