"The subject of the work", wrote Dante in his letter to Can Grande del Scala, "if taken literally, is the state of the souls after death; but if taken allegorically, its subject is how man by the exercise of his free will justly merits reward or punishment." Here at the beginning of the Purgatorio, the two poets (Dante and Virgil) have emerged from the Inferno, where each punishment was simply an expression of the sinful self-will of the one condemned. The road which is before them is one of purgation of the will - of turning the will away from the slavery to habit and sin, and introducing it to true freedom.
At the beginning of their journey they meet Cato, the guardian of Purgatory, so to speak. Virgil assents to Cato's demand for information: how did these two escape from Hell and come to these shores?
"Not on my behalf
have I come here; a lady sent from Heaven
asked me to guide this man along his way.
But since it is your will that we reveal
the circumstances of our presence here,
how can my will deny yours what it asks?" (I.52 ff)
It is worth noting the contrast with the Inferno: rather than "self will" we have the desire to put the will of another first. It is only by grace (the lady sent from Heaven) that Dante has emerged from knowledge of sin to this place of repentance and purification. One of the great themes of purgatory is freedom; only the soul which is purged of sin is truly free. The human will (contrary to what we may think) is actually in bondage. A life of merely "doing what I want" results in less, not more, freedom. And so we have the figure of Cato, Roman statesman, whom Virgil addresses with this theme:
May it please you to welcome him - he goes
in search of freedom, and how dear that is,
the man who gives up life for it well knows.
You know, you found death sweet in Utica
for freedom's sake; there you put off that robe
which will be radiant on the Great Day (I.70 ff)
The images in this canto are of light and the colour of a new dawn. In Dante's elaborate system of astronomy, it is to be understood that the day is April 10 - the dawn of Easter day. The canto gives us a picture of the "tender tint of orient sapphire" (as the sky lightens) and we are told that "the rising sun will show you where to climb" (108).