In Dante's Inferno, sin is a central theme, explored through the structure of Hell and the punishments meted out to sinners. Dante categorizes sin into three main types: incontinence, violence, and fraud, each increasing in severity. The nine circles of Hell reflect these sins, with each circle serving as a punishment for specific transgressions. Dante's journey through Hell is not only a depiction of sin but also a personal exploration of his own moral failings and the possibility of redemption.

The three types of sin in Inferno are incontinence, violence, and fraud. Incontinence involves a lack of self-control, reflecting an absence of God and Christ. Violence includes harm against God, others, or oneself, and is punished more severely. Fraud, the most grievous sin, involves deceit and treachery, using intellect to harm others. This sin is punished harshly, with deceivers like Judas being eternally tortured by Lucifer. Dante's hierarchy of sin underscores the moral gravity of using one's intellect for deception.

The nine circles of Hell further illustrate the theme of sin. Each circle corresponds to a specific sin, from Limbo for the unbaptized to the Ninth Circle for treachery. The circles reflect the severity of sins, with punishments that fit the crime. For instance, the lustful are blown about by winds, symbolizing their lack of control, while the treacherous are frozen in ice, representing their cold-hearted betrayal. This structure emphasizes the consequences of sin and the moral order Dante envisions.

Dante's personal journey through Hell reveals his own sins, such as undue sympathy for the damned, pride, and anger. His guide, Virgil, represents reason and helps Dante confront these failings. The dark forest at the beginning symbolizes sin, with animals representing lust, pride, and avarice. The she-wolf, symbolizing avarice, is the most threatening, highlighting the insidious nature of greed. Dante's journey is a path to redemption, illustrating the choice between following God's will or succumbing to sin.

In Canto 18, Dante critiques the Catholic Church's moral corruption by placing a priest guilty of fraud in Hell. This reflects Dante's anger at deception within the church and underscores the theme of sin as a universal human failing. The presence of clergy in Hell highlights that no one is immune to sin, reinforcing the need for moral integrity. Dante's Inferno serves as both a cautionary tale and a moral guide, urging readers to reflect on their own sins and seek redemption.