The two themes of religion and divine retribution collide in this chasm where the Simonists reside. Simonists, named after Simon the Magus, are souls who sold ecclesiastic favors and offices for their own personal wealth.
These sinners, the Simonists, are upside-down in holes resembling baptismal fonts, illustrating that their sin debased their office, and their feet are on fire, most likely lit by the oil of the last rites. Their time in the font is limited, however. When a new sinner comes, he takes the previous sinner's place, and the previous sinner is shoved down into the rock for eternity, much like the succession of Simonists in office.
These sinners are punished in a manner that is a curious reversal of baptismal practices of the time: Even the burning feet are from the oil used in baptism instead of the cool sweetness of the holy water.
Dante clearly finds these sinners despicable enough to pause in the narrative for a moment and rebuke them harshly. This act does not happen often in Inferno, and it is significant because it illustrates Dante's abhorrence of the corruption of the church that he held so dear. Dante also takes a moment out of the narrative to answer the charge of sacrilege from a number of years earlier when he saved a boy from drowning in a baptismal font by smashing it.
