Commentary Purg XVII 25

There can be little doubt: the notion of these visions as having 'rained down' into the image-receiving faculty of his soul cements the claim made for them.  Here is part of Singleton's comment on this verse (DDP Singleton.Purg.XVII.25): 'The phantasy, or imaginativa, is "lofty" because of the experience of a vision coming from such a source.  For this adjectival usage, cf. "la morta poesì"; [Purg I 7]; "la scritta morta," [Inf VIII 127]; "alto ingegno," [Inf II 7]; and again "alta fantasia" in [Par XXXIII 142].'  It should perhaps be noted that Singleton here probably only rightly contradicts his own previous gloss of 'alto ingegno' at DDP Singleton.Inf.II.7, which he then interpreted as meaning 'the poet's own genius.'  See C.Inf.II.7-9.

      That the poet here uses the very phrase 'alta fantasia,' which will mark his final vision of the Trinity three lines from the end of the poem ([Par XXXIII 142]), underlines the importance of this 'trial run' for his capacity as visionary protagonist (and eventually God-inspired poet).