Commentary Purg XV 28-33

Virgil's promise that eventually Dante's eyes, as his soul becomes more fit for the task, will be able to look upon angelic radiance without turning away is fulfilled at least in [Purg XXX 10] and [Purg XXX 18], where this word for 'angel,' messo (or messaggiero) -- 'messenger,' is next (and for the last time) employed (it was introduced to the poem in [Inf IX 85]).