Commentary Purg XXXII 19-24

The elaborate military simile, in which the vanguard of the Church Triumphant had turned and was already moving eastward while the chariot was still facing west (an effect striven for and achieved by marching bands between the halves of American football games) may have an ulterior purpose.  Dante has reversed temporal order to present first the Church in triumph as it will be after time, and only then the Church in its earthly travail (see C.Purg.XXIX.115-120).  As preparation for that change, from Church Triumphant to Church Militant, he may have chosen this introductory military simile, one in which the forces with which we identify are under attack and in strategic retreat.