Beatrice concludes her speech by expressing the efficacy of Lucy's words on Dante's behalf, which won her over to interceding with Virgil in order to give her beloved a second chance. (Purgatorio XXX and XXXI will reveal that she had grounds for being less charitable to her backsliding lover.) Her speech concludes with the same sort of captatio benevolentiae that marked its inception ([Inf II 58] and C.Inf.II.58), now couched in terms that praise Virgil's parlare onesto. The phrase means more than 'honest speech,' as is made clear by its etymological propinquity to the verb onora (honors) in the next line. 'Noble' (found also in Sinclair's translation) seemed to the translators a reasonable way to attempt to bridge the gap between 'honest' and 'decorous,' retaining a sense of moral and stylistic gravity for the words of the greatest poet of pagan antiquity -- which Virgil was for Dante.
