Commentary Par XXIV 151-154

St. Peter now 'laureates' Dante in Faith.  While the phrase tre volte (three times) occurs on seven other occasions in the poem, its first and last appearances are the only ones that occur in the final four verses of a canto, here and in [Inf XXVI 139].  It would seem possible that this use remembers in bono that first occurrence, in which the ship of Ulysses spins around three times before it sinks.  Here Dante is not being punished for his presumption, but rewarded for his faith.