In a Christmas homily, St. Augustine explained that the invisible Creator was made visible to us through a visible person. God is with us, Immanuel. He chose to take a body out of a virgin body.
If you are interested in more quotes on Virgin Mary, you can find them in Mary and the Fathers of the Church on Amazon in both Kindle and paperback formats.
Gambero, L., 1999. Mary and the Fathers of the Church 1st ed. Translated by Buffer, T., San Francisco: Ignatius Press.