Contrary to now prevalent tendency to read Canti XVI, XVII and XVIII of the Purgatorio in a single block this essay has deliberately chosen the lectura Dantis method in order to reiterate the central importance of this triptych for the whole Commedia. This because an autonomous consideration of each canto in its essential unity of composition allows us to fully evaluate the structure, complexity and scansion of Virgil’s lesson on love. It is a lesson in which the figurative dialectic of teacher and pupil does not appear to translate into an «spettacolo estetico» in accordance with Benedetto Croce’s interpretation. What does appear to emerge is a spiritual movement aimed at clarifying its objective of showing and making understood the genuine novelty, importance and universality of his concept of love in an ordered and clear way. Love is understood here not as the love of troubadour poets, of stilnovismo and Guido Cavalcanti, who emphasised its sensual character, but as the fount of every virtue and every vice, of all good and all evil. Thus even this first part of the lesson indicates a higher plane, very different from what Gianfranco Contini called the «etica mondana» of Vita nuova and a decisive turning point in the context of the thirteenth century debate. Following on from Giovanni Getto who spoke for the Paradiso of «poesia dell’intelligenza» and on the basis of the ancient commentaries, by Buti in particular, this essay puts forward the idea of a poetry of the institutio, of the teaching of the charismatic masters, Virgil here and earlier in the Inferno, Statius, intermediate guide between Virgil and Beatrice, St. Bernard Dante’s last «dottore» on his journey towards God.