"that cruel sea" (Metaphor)
Even the very first lines of the Purgatorio are, in fact, metaphoric. Dante begins the poem by representing his "wit" as a ship that has just left Hell, which, perhaps surprisingly, he represents as a "cruel sea." This metaphor connects to Dante's more wide-ranging motif of navigation and also establishes that this place, the mountain of Purgatory, will be "smoother water."
"As sheep" (Simile)
In canto III, lines 79-84, Dante describes a group of souls as being like "sheep come from the fold, first one, / then two, then three, and the rest stand timid, / bending eyes..." This simile depicts them as a sort of docile flock; importantly, this simile also picks up on the image of Christ as a shepherd and his followers as sheep, seen in John 10:1-21 and elsewhere.
"we are born as worms" (Metaphor)
As Dante sees the penitent prideful in Canto X, he asks if humans cannot "see that we are born as worms, / though able to transform into angelic butterflies..." Although the use of "as" may make you think this is a simile, it here means something closer to "born being worms" rather than "born like worms." As such, Dante is metaphorically suggesting humans are worms, which is to say earthbound, while containing the potential for spiritual ascent and transcendence.
"the sponge" (Metaphor)
As Dante ends his discussion with Pope Adrian V, his curiosity is not fully sated; as such, when he leaves Adrian to his penitence, Dante writes that he "drew the sponge, not full yet, from the water." Here the sponge is being used as a metaphor for Dante's mind. The metaphor emphasizes his desire to soak up all the information he can and helps paint a clearer picture of Dante's almost natural tendency to absorb the stories of others.
The snow (Simile)
In Canto XXX, Dante's emotional outpouring is built up through a long and complex simile, likening his torrent of tears to the water produced when the snows on a mountain melt. This simile emphasizes the violence of his emotion while at the same time using the length of the simile to build up to a climax; in fact, this moment is in a way the climax of the Purgatorio.
