Inferno: Cantos 17-19

Canto 17
"His face was just a man's face, outwardly kind" (pg. 171). The author uses this to emphasize not only the evil that there is in Hell, but also how fake the people were when they were still alive. Right now, Dante and Virgil are in the ring with the sins of fraud, so it only serves to reinforce that idea that the monster's face seems kind when the monster was made to punish the evil for their sins. The demon's deceptively kind, human face lulls souls into a false sense of security before he makes sure that they are tortured as much as they should be for lying their way through life.
Canto 18
"the bridge with all those bound toward St. Peter's, facing the Castle, while those headed..." (pg. 181). Dante uses this to show the difference that there is between the people who did good in their life and those who did evil. The way he portrays these sinners in Hell as going two opposite ways is meant to give a visualization of the way that the sinners and the people who follow God are going two opposite ways. The memory of people heading for St. Peter's is used to show how the character Dante needs to reassure himself that his goal is right. He is only going through Hell in order to gain the ultimate prize of knowledge, as well as being with God. The only way he can truely come befor St. Peter's gates is if he learns about the suffering that he would have to endure if he wasn't an obedient servant to God.
Canto 19
"...a lawless shepherd of the west..." (pg. 195). In most religious views, the shepherd is a symbol of Jesus. I think the author placed this picture of the evil shepherd in Hell in order to show how discouraging it is for Dante to try and travel through the evil without some of it starting to get to him. He feels sympathy for some of the sinners and the punishments that they have to suffer, and starts to wonder if he might have acted in some of the same ways as them. The author put the picture of the evil shepherd in the fradulent ring of Hell in order to show that nothing is as it seems and Dante just has to trust in God in order to be saved from the same fate.