The Divine Comedy, Volume 2, Purgatory

Invocation to the Muses.—Dawn of Easter on the shore of Purgatory.—The Four Stars.—Cato.—The cleansing of Dante from the stains of Hell.
To run over better waters the little vessel of my genius now hoists its sails, and leaves behind itself a sea so cruel; and I will sing of that second realm where the human spirit is purified and becomes worthy to ascend to heaven.
This old man, as soon appears, is the younger Cato, and the office here given to him of warden of the souls in the outer region of Purgatory was suggested by the position assigned to him by Virgil in the Aeneid, viii. 670. “Secretosque pios, his dantem jura Catonem.”
It has been objected to Virgil’s thus putting him in Elysium, that as a suicide his place was in the Mourning Fields. A similar objection may be made to Dante’s separating him from the other suicides in the seventh circle of Hell (Canto XIII.). “But,” says Conington, “Virgil did not aim at perfect consistency. It was enough for him that Cato was one who from his character in life might be justly conceived of as lawgiver to the dead.” So Dante, using Cato as an allegoric figure, regards him as one who, before the coming of Christ, practised the virtues which are required to liberate the soul from sin, and who, as be says in the De Monarchia (ii. 5), “that he might kindle the love of liberty in the world, showed how precious it was, by preferring death with liberty to life without it.” This liberty is the type of that spiritual freedom which Dante is seeking, and which, being the perfect conformity of the human will to the will of God, is the aim and fruition of nil redeemed souls.
In the region of Purgatory outside the gate, the souls have not yet attained this freedom; they are on the way to it, and Cato is allegorically fit to warn and spur them on.
“Who are ye that counter to the blind stream have fled from the eternal prison?” said he, moving those venerable plumes. “Who has guided you? Or who was a lamp to you, issuing forth from the deep night that ever makes the infernal valley black? Are the laws of the abyss thus broken? or is a new design changed in heaven that, being damned, ye come unto my rocks?”