The speaker in Canzone 128 addresses a very pesky problem: the nobility of his country are fighting "vanity wars" with each other and hiring professional, foreign fighters to do their dirty work. The constant state of warfare and the wild, unpredictable natures of the mercenaries have taken their toll on Italy in a big way.
Petrarch asks the elite class to remember their country, to have pity on their neighbors, and think about the judgment that their souls will have to face in the afterlife. In other words, he wants them to use their brains and change their ways.
He also reminds the nobles that they ought to preserve their beautiful homeland by guarding it from foreign invasion (rather than welcoming it with open arms). Petrarch finally addresses the poem itself, telling it to behave nicely when it goes among the "haughty" princes, since they are rash and rude. Only then might it have a chance to beg for peace.