I think that this song is about Lúthien's love for Beren. She was an Elf, immortal, but he was a mortal Man. Her love unbreakble for him meant that she had to give up the eternal life of the Eldar, "High's the fee" and spend her remaining years living with Beren, "Soon my spirit will return" (as a mortal).
From Beren and Lúthien the kings of Númenor and of Arnor and Gondor of the Third Age were descended.
I think that this song is about Lúthien's love for Beren. She was an Elf, immortal, but he was a mortal Man. Her love unbreakble for him meant that she had to give up the eternal life of the Eldar, "High's the fee" and spend her remaining years living with Beren, "Soon my spirit will return" (as a mortal).
From Beren and Lúthien the kings of Númenor and of Arnor and Gondor of the Third Age were descended.