Thomas Aquinas said of allegory that it is useful both to present spiritual truths to those accustomed to thinking only in the terms of sensual reality and, simultaneously, to hide them from the unworthy (St. I.1.9 res 3). In the first two canticles of the Comedy (Inferno and Purgatorio) Dante has a strong physical-sensual image: the Earth. Spiritual realities are described in terms of movement in physical space. In Inferno the pilgrim descends into a pit, in Purgatorio, he climbs a mountain. In Paradiso, the central image is light, which is, no doubt, sensual but not really physical. It is, in fact, psychical. In Paradiso, Dante's mystical-metaphysical concerns come to the fore.
He begins Paradiso 2 with a warning: those struggling to follow him (who have not partaken of the "bread of angels") should put the book down NOW (he will not be responsible for lost luggage). Moreover, those who think themselves capable of following had better keep up (there are no maps to where he is going and no place ask directions). Then, to reenforce his warning, the canto continues with Dante and Beatrice landing on the moon and getting into an abstruse disputation about the "moonspots" including a Fourteenth Century map of the cosmos and experiments you can do at home. I admit to my shame and chagrin that I have, more than once, been forced to submit and put the book down.
Which is why I recommend this book. The point of allegory, after all, is its subtext and this book shines in conveying you past the surface conversation to what Dante and Beatrice are really talking about (if you believe they are "really" discussing "moonspots," Moevs can't help you).
Also, if you like, you can check out my author's pageDante's Journey: A Field Guide to the Infernal Regionsand keep a look out for my new book on Purgatorio which will be out shortly.