Dante and Virgil arrive in the third trench, which holds Simonists, those who bought or sold sacred things like the sacraments, church offices, or pardons. Dante praises God's judgment as he sees that the stone here is dotted with many holes, into which the Simonists have put their heads and torsos, with their legs and feet sticking out. The ground flickers with flames, burning the soles of their feet. Dante thinks the holes look like the circular "holes" that priests stand in to conduct baptisms and remembers how he once broke one in order to save a child who was trapped in it.
Now we can see Dante beginning to change. Instead of pity, he reacts to the suffering of the Simonists with satisfaction. To some this may seem cold or cruel, but in Dante's understanding of the world, one should not pity or regret the punishment that God wisely deals out to the sinners who deserve it.
Dante asks who one of the souls is, who seems to be burned even worse than the others. Virgil takes him down closer to the Simonists, and Dante asks the sinner who he is, saying that he feels like a friar about to receive a confession. The sinner thinks that Pope Boniface is talking to him, and he bitterly asks if he has died already. Virgil has Dante tell the sinner that he is not Boniface and the sinner identifies himself as Pope Nicholas III. He says that other Simonists are buried deeper in the hole and that when his successor Boniface comes, he will take his place, pushing Nicholas down further into the hole.
With this scene, Dante is able to use his journey through hell to comment on and deeply criticize the Catholic church of his time. Nicholas III was pope when Dante was a boy. By placing a Pope among the Simonists Dante is condemning the Catholic Church as a whole for trading in cash (for instance, the sale of indulgences) in specific, and for seeking secular power in general. Dante felt the Church and State should be separate, and that the Church should actively avoid secular power. Dante did strongly hate Pope Boniface, who worked to get the Black Guelphs into power, resulting in Dante and other White Guelphs being exiled from Florence.
Pope Nicholas predicts that after Boniface there will be an even more evil pope. Dante chastises Nicholas, asking him how much Jesus charged Peter for the keys to the kingdom of heaven (nothing). He tells Nicholas that he deserves his punishment and says that he would use even harsher words if he didn't have so much respect for the papal office. He tells Nicholas that he has treated gold and silver as divine, instead of God. Upon hearing this, Nicholas writhes more and more in pain. Virgil approves of Dante's harsh speech and carries him back up to the path leading to the next trench.
Dante continues to use the character of Pope Nicholas to criticize the church of his time. He is here essentially telling Nicholas that he and others in the church who want earthly wealth and power have established money as their God rather than worshipping the true God. Far from pitying Pope Nicholas, Dante takes this opportunity to increase his suffering, showing that he piously approves of Nicholas' deserved punishment. Virgil, meanwhile, approves of Dante's growth in piously approving of the treatment of sinners.