Commentary Purg XIX 133

Adrian's response is so urgent that he only gets to his fraternal salute, nearly always found, elsewhere in the poem, at the beginning of direct address and never at its end, last.  His 'frate,' rhyming with 'dignitate,' is the answer to the hierarchy underlined by that second term and by Dante's kneeling.  In God's kingdom there is no specialness, only brotherhood of the equally special.

      For a survey of the presence of the address 'frate' in the Commedia, see C.Purg.IV.127.  There are twenty occurrences of the word, when used to address another, in the poem, the first in [Inf XXIII 109], where Dante addresses the Jovial Friars rather nastily, the last in [Par XXII 61], where Benedict addresses Dante, who is saluted a total of seventeen times in this way.  Only Forese Donati (twice) and Beatrice (four times) use this form of address more than once.  In the last two cantiche the only addressee other than Dante is Statius ([Purg XXI 131]), in Virgil's humble and warm disclaimer of a respect similar, on Statius's part, to that displayed here by Dante for Adrian.