Mount Purgatory is conically shaped. Virgil and the Pilgrim will ascend the mountain by circling upwards through seven terraces. Each terrace corresponds to one of the Seven Deadly Sins: Pride, Envy, Wrath, Sloth, Greed, Gluttony, and Lust. On each terrace, Virgil and the Pilgrim will encounter the faithful souls who are being purged of these sins. Once purged of a sin, the soul moves upward, to the terrace above, to be purged of the next sin, ever upward toward the summit. On the summit of Mount Purgatory is the Garden of Eden, the earthly paradise. Above Eden, in the heavens, is Paradise where God dwells.
In short, the upward journey of purification is a journey upward toward God. This, then, is the plot of The Divine Comedy, one person's journey toward God. Having seen the punishments of the damned in hell, the Pilgrim will now make the climb toward God. But it's going to be a hard climb. While the Pilgrim simply witnessed the punishments of the damned, his journey on the slopes of Mount Purgatory will involve confronting and being purged of his sins.
On the shores of the island where Mount Purgatory stands, in Canto I of Purgatory Virgil summarizes the journey he's taking the Pilgrim on, how grace came to the Pilgrim in the nick of time to save him and take him on this journey:
This man has not seen his final hour,When we make the climb toward God, when we face and confront our sins, we go in search of freedom. And the climb is enabled by the prevenient grace of God.
although so close to it his folly brought him
that little time was left to change his ways.
So I was sent to help him, as I said:
there was no other way to save his soul
than by my guiding him along this road.
Already I have shown him all the Damned;
I want to show him now the souls of those
who purge themselves of guilt...
How we came here would take too long to tell;
from Heaven comes the power that has served
to lead him here to see and hear...
...he goes in search of freedom...
From Heaven comes the power to lead us on the way.
