The Christmas season celebrates, as we all know, the birth of Jesus. But it is also one of the few times in the year when Christians think and talk about Mary, his mother. An ubiquitous fixture in crèches and the undoubted lead in Nativity plays, the Christmas story is in some ways as much about Mary as it is the Christ child. But very little is known about the young woman who religious tradition remembers as the “mother of God.” Centuries of careful theological...