This. This is my favorite AR/ABDL/Infantilist story, period.
Being a fan of the Divine Comedy, the title is what drew me in, but the plot is what kept me reading. Dante's journey - from selfish, immature child to selfless, good man - is a perfect character progression, with a definite redeeming factor. That alone would've made the story perfect, but you went a step further and redeemed Lysa, too - with her own talents, even though they seem to be "bad" talents.
The ending was wonderful - the promotion from Limbo was perfect for Lysa, absolutely wonderful. I like the way that she proves herself as mature, not by blindly listening to what she is told, but by exercising her own will and reason - it demonstrates a philosophical point, that the goodness of a person isn't determined by how well they can parrot a bible study, but by their ability to come to good decisions, thinking for themselves.
Dante's ending was more bittersweet, but I liked it - the newly demonic nature of "Lucy" isn't so different than her usual nature, demonstrating the ultimate fallibility of any plan that isn't fully divine, which was a nice touch.
Going back to the comment about the Divine Comedy, I found it deliciously ironic that your Limbo/Purgatory almost seemed better suited to be Dante's Inferno - the lack of redemption, the descent into infancy, the cruel, swift punishment - all of it screamed "Inferno" in the midst of Limbo. In fact, your Dante even had a "Virgil" of his own - Lysa.
Speaking of Virgil, the "Orpheus" bit was perfect. The myth of Orpheus is actually one of my favorites, and I can't help but prattle a bit about how perfectly you captured it - first, ironically, one of the most famous versions of the Orpheus myth is actually from Virgil. But, Orpheus' story is an interesting one - he loses Eurydice not once, but twice - just as Dante lost his self not once, but twice - once to despair, and once to angel's milk. But, Lysa turned out to be the one closest to the character of Orpheus. Orpheus was granted the chance to save Eurydice because he was able to move the hearts of the jailers of Hades - just as Lysa was able to move St. Jude's heart.
The one thing I find myself wishing for is a sequel - either of Lisa's journey into full sainthood, or Dante's journey our of Hell, perhaps with Lysa's help from heaven. Then again, who's to say it wouldn't lessen the impact of Dante's sacrifice? Whatever you decide to do, I'll be looking forward to seeing more from you!