Why Tolkien Called the Story of Beren and Luthien "the Kernel of the Mythology"

There’s a Great Dance throbbing at the heart of the world

The story of Beren and Luthien is, according to Tolkien, the “kernel” of his mythology, and it starts with a dance of enchantment.

Beren chances upon Luthien,

as she danced upon the unfading grass in the glades beside Esgalduin. Then all memory of his pain departed from him, and he fell into an enchantment; for Lúthien was the most beautiful of all the C…