'Still in Her Darkness Doth Erin Lie Sleeping'

I was first introduced to this poem by the lovely musical setting performed by the Irish vocal group, Anúna. It appears on their self-titled album under the title, ‘Silent, O Moyle’, and includes this short mention in the liner notes: ‘Thomas Moore (1779-1852) was a household name in Europe in the 19th century. This beautiful melody tells the story of the Children of Lir and is one of his finest songs.’ Here is the text as it appears—under the title, ‘The Song of Fionnuala’—in the wonderful book, The Poetical Works of Thomas Moore, Reprinted from the Early Editions with Explanatory Notes, etc., illust. Garrett, et al. (NY: Thomas Y. Crowell & Co., 1888), p. 224:

Silent, O Moyle, be the roar of thy water,
Break not, ye breezes, your chain of repose,
While, murmuring mournfully, Lir’s lonely daughter
Tells to the night-star her tale of woes.
When shall the swan, her death-note singing,
Sleep, with wings in darkness furl’d?
When will heaven, its sweet bells ringing,
Call my spirit from this stormy world?
Sadly, O Moyle, to thy winter-wave weeping,
Fate bids me languish long ages away;
Yet still in her darkness doth Erin lie sleeping,
Still doth the pure light its dawning delay.
When will that day-star, mildly springing,
Warm our isle with peace and love?
When will heaven, its sweet bells ringing,
Call my spirit to the fields above?

The Crowell edition includes the following explanatory note on this poem, apparently by Moore himself:

To make this story intelligible in a song would require a much greater number of verses than any one is authorized to inflict upon an audience at once; the reader must therefore be content to learn in a note, that Fionnuala, the daughter of Lir, was, by some supernatural power, transformed into a swan [along with her siblings, say other sources], and condemned to wander, for many hundred years, over certain lakes and rivers in Ireland till the coming of Christianity, when the first sound of the mass-bell was to be the signal of her release. I found this fanciful fiction among some manuscript translations from the Irish, which were begun under the direction of that enlightened friend of Ireland, the late Countess of Moira. (p. 224, n. 4)

Thus explained, I thought this poem a remarkable imagining of a sort of messianic expectation in pre-Christian Ireland. Obviously, however, ‘day-star’ should really be capitalised.