Petrarch hopes that the Italian nobility will soon have a change of heart and stop waging war on each other, but he's got to pull out all the stops to ensure that they'll hear what he says. So he calls on Death and Judgment to help him out a bit.
In lines 100-102, he pulls a Charles Dickens on them and shows them the bleak future:
Now you are here, but think of your departure: the soul, alone and naked, one day will come to face the perilous pass.
Petrarch has most likely grabbed the image of the "perilous pass" from Dante (Purgatorio) to help him talk about the difficult journey that the soul faces on the way to judgment before the throne of God. In this scenario, the perilous pass is a real place (check out Gustave Dore's imagining) of it) that can't be traveled without moral strength.
So, what's the point of all this? Petrarch wants to tell the nobles that they are going to have a hard time getting to Paradise after death if they don't straighten up and fly right. If that doesn't help them take their civic responsibilities seriously, we don't know what will.