Dante and Virgil reach the edge of a cliff overlooking the descent to the lower parts of hell, whose overpowering stench Dante can already smell. The two poets take a break in their journey and see a vault with these words written on it: "I hold Pope Anastasius, / Lured by Photinus from the pathway true," (10.8-9). Virgil tells Dante that they should rest here until they are accustomed to the foul stench of the lower circles of hell.
As the vault holding Pope Anastasius shows, even popes can sin and find themselves punished by God—and later Dante will show some other Popes in hell who were more contemporary with Dante's life. The constant foul stench of the lower parts of hell emphasizes its strangeness and difference from Dante's earthly world.
While they are waiting, Virgil explains some of the geography of hell. Looking down into the abyss, Virgil says that there are three circles of hell within the cliffs leading downwards, all filled with damned spirits. Virgil says that all wrongs against heaven end up getting punished. According to Virgil, God hates fraud and deceit the most, so the fraudulent inhabit the lowest parts of hell.
Virgil instructs Dante in God's divine plan of justice. The layout of hell is extremely specific, with more heinous sins getting the more serious punishments that they deserve deeper in hell. Fraud is the most hated sin because it stands most in contrast to love: fraud or deceit breaks the bonds of love by destroying trust.
In the seventh circle of hell, says Virgil, souls are punished for sins of violence. They are divided into groups based on who they have harmed: other humans, themselves, or God. In the first group are murderers, robbers, and plunderers. In the second are those who "their own lives or their own goods destroy," (11.41) by committing suicide or by gambling and wasting away their property. The third group includes those who curse, deny, or defame God, as well as usurers and followers of Sodom.
This division and organization of sinners within hell's different areas is crucial to the idea of divine justice offered by Dante. Hell is not a place of random violence, but rather an organized system whereby sinners get the very particular punishments they need. That order is based upon the central importance of God. Harming God is thus the worst category of offenses. Harming oneself is considered worse than harming others because it involves harming a gift that God gave to you: your life and soul.
Virgil continues to explain the layout of hell in the lower circles full of frauds: in the eight circle are "hypocrites, flatterers, dealers in sorcery, / Panders and cheats, and all such filthy stuff," (10.58-59). The ninth circle contains those who are guilty of even more serious fraud and betrayal. At the very core of Dis are traitors. Dante asks Virgil why hell is arranged in this way, with some damned souls suffering outside of Dis.
At this point, Dante does not fully understand the reasoning behind God's design of hell. Virgil will then instruct him (and the reader).
Virgil calls Dante foolish and reminds him that, as Aristotle teaches in his Ethics, there are three kinds of sin: incontinence (inability to control oneself), vice, and bestiality (violence). Those outside of Dis have committed the first, less serious wrong, and so suffer slightly less than their counterparts within Dis.
As Virgil explains, the divisions of hell are directly related to the different kinds of possible sins, which require different kinds of suffering.
Dante then asks Virgil why usury (money-lending with excessive interest) is so wrong. According to Virgil, humans are supposed to follow nature, as made by God. A usurer makes a life not from nature or labor, but from charging interest on other people's profits and thus scorns nature. Virgil then tells Dante that it is time for them to resume their journey.
This slight digression exemplifies an understanding of sin as any deviation from God's design or plan as manifest in nature. (In this case, usury contradicts the natural way of making a living from working the land.)