Lo How a Rose Ere Blooming

So have you heard this song? I was completely unaware of it until this year when I got three different renditions (Sufjan Stevens, Feist, MoTab) on three different holiday mixes from three different people. And some kids in my ward sang it quartet-like for our Christmas program on Sunday. (This was gorgeous by the way.) Renditions range from the almost medievally classical sounding to folksy and acoustic. The hymn is one of those that can handle the range--deeply biblical with great, simple harmonies.
The line that keeps coming back to me is "Isaiah twice foretold it," and I'm not certain why. Perhaps because this idea manages to be both epic and intimate. That is, we're talking about Isaiah here which automatically gets you credibility points both for style and for doctrine. But we talk about him in a really specific way--not about the overarching and intense prophecies, but about two finite and specific prophecies. We get a glimpse of the writerly Isaiah maybe is the appeal?
Also, just in general, the song is very beautiful. I love the symbolism and going through the same conscious exercise to unpack it as believers have done for millennia. Also, the visual of a rose blooming--the visual of the night and the stable and Mary's face and Joseph's face lit radiant by the light of the star or the light of the child. The rose blooming and casting about it light and love and peace. Thanks Isaiah.