How we cite our quotes: (Line)
Quote #1
[...] and there the truth divine
be heard through me, unworthy as I am (15-16)
Petrarch speaks not only of the duty of princes, but also of the obligations of the poet. It's really his job to tell it like it is—even if the lords don't like what they hear. It's also a way for Petrarch to wiggle out of the nobility's wrath when they realize he's dissing them.
Quote #2
I speak to tell the truth,
not out of hate or scorn for anybody (63-64)
And again, Petrarch is going with the truth thing. He's trying to show that he doesn't have an ulterior motive—like political or monetary gain—in the writing of this poem. He wants the nobility to know that he has to speak as he feels, because things are bad.
Quote #3
From dawn to tierce examine
yourselves, and you will see that one who thinks
himself so cheap cannot hold others dear (71-73)
For one thing, Petrarch says to the Italian princes, you've got a duty to meditate on your motives for wreaking such havoc. It's also their burden to consider the lives of their subjects and neighbors before they make the decision to bring foreign hostile forces into play.