I would add that the number 3 also structures Dante's Comedy and its symbolism is of crucial importance as it represents the Holy Trinity. The structure of the poem is based on the recurrence of the number 3: the meter is the "terzina" or "terza rima" formed by 3 stanzas made of of 3 hendecasyllables rhyiming ABA BCB CDC. There are 33 cantos divided into the 3 cantiche (Inferno, Purgatorio and Paradiso). Yet, the Inferno has one additional canto which functions as a general prologue to the whole book. This makes the number of all cantos 100, the perfect number.
In the Middle Ages numbers were given great significance, and were thought to reveal the mysteries of God's creation. The number 100 symbolized for Dante the totality and perfection of the universe. The number 10 is considered to stand for perfection, because it is the base on which the number system is built. The number 100, then, is the perfect number multiplied by its own perfection.