Edith is to Luthien as JRRT is to... Beren?

[Legolas]

Maybe Tolkien was no great warrior, but he found himself in Beren's situation. His admiration for his wife was deep, and describing her as Luthien implies he shared Beren's enviable fate of witnessing/sharing her beauty. Their stories parallel in several ways.

Compare this description of Luthien from Chapter 19 of The Silmarillion with a poem Tolkien wrote about his wife (shared by Carpenter in his Tolkien biography).

It is told in the Lay of Leithian that Beren came stumbling into Doriath grey and bowed as with many years of woe, so great had been the torment of the road. But wandering in the summer in the woods of Neldoreth he came upon Lúthien, daughter of Thingol and Melian, at a time of evening under moonrise, 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 Children of Ilúvatar. Blue was her raiment as the unclouded heaven, but her eyes were grey as the starlit evening; her mantle was sewn with golden flowers, but her hair was dark as the shadows of twilight. As the light upon the leaves of trees, as the voice of clear waters, as the stars above the mists of the world, such was her glory and her loveliness; and in her face was a shining light.

But she vanished from his sight; and he became dumb, as one that is bound under a spell, and he strayed long in the woods, wild and wary as a beast, seeking for her. In his heart he called her Tinúviel, that signifies Nightingale, daughter of twilight, in the Grey-elven tongue, for he knew no other name for her. And he saw her afar as leaves in the winds of autumn, and in winter as a star upon a hill, but a chain was upon his limbs.

There came a time near dawn on the eve of spring, and Lúthien danced upon a green hill; and suddenly she began to sing.

Lo! Young we are and yet have stood
like planted hearts in the great Sun
of Love so long (as two fair trees
in woodland or in open dale
stand utterly entwined and breathe
the airs and suck the very light
together) that we have become
as one, deep rooted in the soil
of Life and tangled in the sweet growth.

Tolkien's experiences with Edith echo through the circumstances around Beren and Luthien. Tolkien was an exile; Beren was separated from his parents as well - his mother fled with family to safety, his father slain. Tolkien was younger than Edith; Beren was younger than Luthien.

They had to deal with the pain of disapproving parents. Tolkien met Edith at 16 and they began a relationship, but his guardian forbid him to see her until he was 21 because she was Anglican, and a distraction from schoolwork. Thingol was "filled with anger" when he found out Luthien was meeting Beren, a mortal, in secret.

Tolkien's years of waiting to resume his relationship with Edith also remind me of Beren's dumb spell in the woods after he saw Luthien. Wandering alone, he caught sight of her in the summer, and was left there looking for her until the eve of the next spring. (Quoted above.)

Soon after finally finding Luthien, Beren meets Thingol and is sent away to retrieve a Silmaril alone. Likewise, Tolkien was sent off to World War I just months after marrying Edith.

A couple of years later while stationed in England again, a walk together inspired the account of Beren and Luthien's first encounter.

Tolkien explains this in Letter 340, which was written to Christopher after Tolkien had decided on Edith's grave inscription. He says, about the inscription:

I have at last got busy about Mummy's grave. ... The inscription I should like is:

EDITH MARY TOLKIEN
1889-1971
Luthien

: brief and jejune, except for Luthien, which says for me more than a multitude of words: for she was (and knew she was) my Luthien.

July 13. Say what you feel, without reservation, about this addition. I begin this under the stress of great emotion & regret - and in any case I am afflicted from time to time (increasingly) with an overwhelming sense of bereavement. I need advice. Yet I hope none of my children will feel that the use of this name is a sentimental fancy. It is at any rate not comparable to the quoting of pet names in obituaries. I never called Edith Luthien - but she was the source of the story that in time became the chief pan of the Silmarillion. It was first conceived in a small woodland glade filled with hemlocks in Roos in Yorkshire (where I was for a brief time in command of an outpost of the Humber Garrison in 1917, and she was able to live with me for a while). In those days her hair was raven, her skin clear, her eyes brighter than you have seen them, and she could sing - and dance. But the story has gone crooked, & I am left, and I cannot plead before the inexorable Mandos.

He goes on to tell Christopher that he'd like to talk to him, to tell him all about he and Edith's relationship. He mentions them healing one another; in the story, Luthien and Huan healed Beren twice.

I say no more now. But I should like to ere long to have a long talk with you. For if as seems probable I shall never write any ordered biography - it is against my nature, which expresses itself about the things deepest felt in tales and myths - someone close in heart to me should know something about things that records do not record: the dreadful sufferings of our childhoolds, from which we rescued one another, but could not wholly heal the wounds that later often proved disabling; the sufferings that we endured after our love began - all of which (over and above our personal weaknesses) might help to make pardonable, or understandable, the lapses and darknesses which at times marred our lives - and to explain how these never touched our depths nor dimmed our memories of our youthful love. For ever (especially when alone) we still met in the woodland glade, and went hand in hand many times to escape the shadow of imminent death before our last parting.

In my edition, there's an asterisk by the line "(and knew she was)" that explains that Edith knew the early version of Beren and Luthien's story, as well Aragorn's song in Lord of the Rings, were about her.

Sorry for the essay, but hopefully it explains his deeply personal attachment.