When we fall, sometimes we fall really hard and can barely get up again. Hitting the bottom shatters everything in you and you might wonder how can these pieces be remade again?
When Dante finds himself in the dark wood, he is shattered. As he travels through Hell, he is wearied greater and greater as he descends.
But when he finds himself a the bottom of Mount Purgatorio, he begins to ascend. Humility lightening his step. As he and Virgil ascend, the way becomes easier and he gains strength as he goes.
This is the workings of grace and mercy and divine love. Only what God gives us can strengthen us. What is undeserved is what makes us ascend.