Письма Рождественского Деда

The style feels so warm and genuine—I'm curious whether Tolkien imagined these as real letters or crafted them entirely for the story. What inspired this format?

The illustrations and stories evoke such a cozy holiday magic—did Tolkien draw from his own childhood memories or create a completely fictional world?

It gives a sense of ongoing tradition, but I wonder if this structure was meant to emphasize the passing of time or the evolving relationship between Tolkien and his children.