Not surprisingly, Pope Francis sees the human fulfillment of his encyclical in Mary, the mother of our Lord.
Somewhere it has to work, otherwise faith is only dangling doctrine. But if there is an example to whom we can turn in order to see the principle personified, then we dare to believe we can be among those who embody and express the light of faith.
No matter what we may think about the adoration of Mary, we can all agree that she was a woman totally abandoned to God. As such she became a witness to the light of faith, and as such she encourages us to go and do likewise!