| Quote #4
And here my memory defeats my wit:
Like all of the souls in Paradiso, Cacciaguida can read Dante's mind. This means that Dante's voicing of his questions is unnecessary. Thus, the telepathy of the blessed renders Dante silent. A minor theme in Paradiso is speaking only at the proper time; this makes silence an appropriate counterpoint to effective speech.
| Quote #5
If here below, where sentiment is far
The "you" that Dante makes such a big deal of is the Italian voi, only used to address a social superior, like a noble. The superstition that "Rome was the first city to allow [this word]" points out the city's insufferable pride, in thinking its inhabitants the only ones deserving of such a title. This ties into Dante's perception of the Holy Roman Church (centered at Rome, of course) as hopelessly corrupt. Beatrice's smile, which is compared to "the woman who had coughed … at Guinevere's first fault" is her snide way of pointing out the irony of Dante's situation: even though he looks down on Rome for using voi, he himself has used it when referring proudly to his noble bloodline.
| Quote #6
so, with a voice more gentle and more sweet –
Dante makes a few observations on language in this passage. First, Cacciaguida's speech is "more gentle and more sweet [than] our modern speech," suggesting that, in the past, language was better than it is now. Also, notice that Cacciaguida only speaks about his noble ancestors in these few lines, and only at Dante's request. He much prefers, it seems, to not talk about them ("of that, / silence, not speech, is most appropriate") because he does not want to sound too proud.