The Fellowship of the Ring by J.R.R Tolkien (Harper Collins 1991) pp. 227-30
Frodo gradually emerges from “a dream of music that turned into running water, and then suddenly into a voice”. And the voice is that of Bilbo chanting verses.
Eärendil was a mariner that tarried in Arvernien; he built a boat of timber felled in Nimbrethil to journey in; her sails he wove of silver fair, of silver were her lanterns made, her prow was fashioned like a swan, and light upon her banners laid.

And so begins the longest poem in The Lord of the Rings. A poem that links the story both to The Silmarillion and to the moment in 1914 when first Tolkien began to conceive his legendarium, the moment in which his heart was captured by the beauty of some lines from an Anglo-Saxon poem.
” Eala earendel, engla beorhtast, ofer middangeard monnum sended…”
“O, Earendel, brightest of angels, sent to men above Middle-earth…”

The poem was entitled, Christ ,or The Advent Lyrics and as soon as we read the word, Advent, we know that these words are an expression of profound longing, a cry from the darkness of our prison, a longing for freedom and for peace.
The poem continues, “You come yourself to illuminate those who for the longest time, shrouded in shadow and in darkness here, reside in the everlasting night- enfolded in our sins, they have had to endure the dark shadows of death.”
It all fits because the tale that Bilbo tells in his poem is one of deliverance from darkness. Eärendil journeys from Middle-earth to Valinor to plead for aid against Morgoth who has conquered all. Gondolin has fallen. Nargothrond has fallen. Doriath has fallen. All that was most beautiful has been lost for ever.
But that is not all. The darkness does not belong to Morgoth alone. The sons of Fëanor, bound by the oath that they swore to their father in their grief and fury, attack Arvernien seeking for the Silmaril, seized from the very crown of Morgoth by Beren and Lúthien Tinúviel. Even the reverence in which the memory of Beren and Lúthien is held is not enough to restrain the revenge required by this oath. But Eärendil still goes to Valinor seeking mercy for all and Manwë, Chief of the Valar, of the Ainur, the makers of the Music, allows this one emissary to enter the Undying Lands. Eärendil, the great intercessor, brings aid to Middle-earth in its darkest hour. “The looked for that cometh at unawares, the longed for that cometh beyond hope.”
And Eärendil will come once more in The Lord of the Rings in Shelob’s Lair, when in his darkest moment, in darkness visible as death bears down upon him, Frodo holds high the star-glass of Galadriel in which the light of the Silmaril is held and cries out, “Aiya Eärendil Elenion Ancalima!” Hail Eärendil, Brightest of Stars! The very same Advent cry that Tolkien read in 1914 and which captured his heart.

“It all seemed to me to fit somehow.”
The sense in which the story fits, both in the Hall of Fire in Rivendell and in Shelob’s Lair in Mordor is that Frodo has been drawn into the age-old longing of the Children of Ilúvatar for a light that will never go out, that darkness can never overcome.
“O Morning Star! Come and Enlighten those who dwell in darkness and the shadow of death”.
“O Oriens…Veni et inlumina sedentes in tenebris et umbra mortis”.
Those who sit at ease are not in need of deliverance. The story that seems to fit somehow is the age long story of the prisoner in darkness. Bilbo and then Frodo are drawn into this story. Bilbo becomes a member of Thorin Oakenshield’s party. Frodo sets off into the wild with his three companions. Both are linked together by the finding of the Ring of Power. Both are linked together too by a desire for adventure. Soon all who have been drawn into this story, all who have been brought to Rivendell at this moment, at the coming of the Ring and the Ringbearer, will gather together to take counsel for the deliverance of Middle-earth. And once again the prayer of Eärendil will be made by those who sit in darkness and the shadow of death.