Commentary Par IV 28

Indicating only the highest rank of angels, the Seraphim, Beatrice reminds Dante that all the nine ranks of angels are in the Empyrean and are the beings closest to God.  Here the poet resolves a potential problem, similar to that caused by the appearance of the souls in the spheres, in that readers might eventually assume that the angelic order most associated with a certain heaven actually dwells in that heaven.  This verse cancels that potential reading before it can be applied.