Dante understands Saint Lucy. For him, she is "the enemy of everything cruel." He presents her as an essential mediator of heaven's help in Canto II of the Inferno.
Beatrice is the one who descends to Limbo to commission Virgil to serve as the wayfaring Dante's guide. Virgil recounts how this all came about because Dante is about to lose his nerve for traveling through the worlds on the other side of death, and Virgil wants him to know that love surrounds him and directs his way out of the dark wood of his life. (The translation I have to hand is Lombardo's.)
Beatrice does not gush, but she loves Dante, who has always loved her, who has loved her into the bright world on the other side of death. And her love has gained the objectivity of heaven, which is stronger than death and hell: "loved moved me to do this, love makes me speak."
Beatrice's personal love for Dante has been so elevated, it descends from the heart of the Trinity through a series of female mediators beginning with Mary. And descending love is mercy:
"There is in Heaven a gracious Lady
with such pity for the plight to which I send you
that the strict decree above has been broken.
This Lady summoned Lucy and said to her:
'Your faithful one now stands in need of you,
and I deliver him into your care.'
And Lucy, an enemy of everything cruel,
arose and came to me where I sat
with venerable Rachel, and said to me:
'Beatrice, true glory of God,
why do you not to go that man's aid
who left the common crowd for love of you?
Do you not hear his pitiful lament
or see how he is threatened by death
in the flood that outswells even the sea?'
No one on Earth was ever so quick
to gain an advantage or escape from harm
as I was then upon hearing these words."
If what Dante says here is thought together with the second matins reading for the feast day (from Saint Ambrose's On Virginity), we see why love must travel through all the worlds.
The problem is that love must first cling to Jesus, if it is to be love. And Jesus is always on the move: "The Word of God moves swiftly; He is not won by the lukewarm, nor held fast by the negligent. Let your soul be attentive to His word; follow carefully the path God tells you to take, for He is swift in His passing."
Why is divine love so difficult to lay hold of? Because the only way to attain a beloved who is above you is for your love to be stretched to the measure of the higher. When this proportioning is to the beloved God, it's called sanctification. In any human love, proximity to the beloved is attained through an analogous process of dying to self. Unless we suffer, we cannot love well.
So, to stretch our hearts, Jesus leads us through the desert, to break our hearts, to break them open: "What does [Christ's] bride say? 'I sought Him, and did not find Him; I called Him, and He did not hear me.' Do not imagine that you are displeasing to Him although you have called Him, asked Him, opened the door to Him, and that this is the reason why He has gone so quickly; no, for He allows us to be constantly tested."
Now, that's one reason the divine Beloved cannot be simply laid hold of: we need to undergo the purgation of a lifelong courtship. So, the first reason for the desert is our own need for purification.
But this is inseparable from the second reason for the desert: solidary love. Why is Jesus moving swiftly? Because He has a burning love to love every single person: "When the crowds press Him to stay, what does He say in the Gospel? 'I must preach the Word of God to other cities, because I have been sent for that.' But even if it seems to you that He has left you, go out and seek Him once more."
And this is relevant for tomorrow's feast of Saint John of the Cross: the dark night, the dark wood, the wilderness, the desert, the hell of our lives is two things simultaneously: purification and solidarity. It is the stretching, and breaking, and opening of our hearts. AND it is solidarity with all the others in darkness. And it is the former precisely by being the latter. We are only purified if we are following Christ as He goes about descending into the hell of each person's life, in merciful solidarity.
And so Saint Ambrose sums it all up: "If you also, like the bride, wish to hold [Christ] fast, seek Him and be fearless of suffering. It is often easier to find Him in the midst of bodily torments, in the very hands of persecutors."
And so we are back to the charity of Saint Lucy, and of all our friends in heaven, who in their solidary love for us can harness romantic love and send it into hell to rescue cold and closed hearts wandering in fear.
And the very love of heaven begins to set these hearts on fire, one by one. And a light begins to grow on this darkling plain.
Saint Lucy, pray for us!