Commentary Par XVII 78

What does Dante imagine Cangrande will accomplish politically?  Somehow, he apparently must think, Cangrande will finish the task that Henry started but failed to complete, the re-establishment of conditions leading to the refounding of Aeneas's Rome.  That is the only surmise possible that might justify the amazingly positive things said throughout this eventually unexpressed (or better, suppressed [see [Par XVII 92-93]]) prophecy.  It is not, perhaps, 'officially' one of the three 'world prophecies' that appear, one in each cantica (Inf. I, Purg. XXXIII, Par. XXVII), but it reflects the first two of them and informs the third.

Scartazzini (DDP Scartazzini.Par.XVII.92) makes the following observation about the series of major prophecies: In Inferno I and Purgatorio XXXIII (he might have added Paradiso XXVII) Dante leaves us in doubt about the identity of the one who will come to set things right, while here he tells us who he is, but not what he shall do.