"Hail the blest morn when the great Mediator down from the regions of glory descends." The song describes the baby Jesus's humble birth and the feeble gifts they offer him. "Brightest and best of the sons of the morning, Dawn on our darkness...."
Earlier editions of this index credited this piece to Reginald Heber (1783-1826), on the basis of Irwin Silber's _The Season of the Year_. Ian Bradley's _The Penguin Book of Carols_ also attributes the song to Heber, and says it was the first hymn he wrote. The _New Oxford Book of Carols_ , however, credits the arrangement to William Walker, while submitting that the "refrain and vv. 2-4 [are] after Reginald Heber." But Spaeth, in _A History of Popular Music in America_, places the whole thing in the hands of Walker.
George Pullen Jackson does not mention either Walker or Heber; he finds it first in William Caldwell's 1837 _Union Harmony_ (but it's not clear whether this is text or tune or both).
The phrase "sons of the morning" is thought to have been inspired by Isaiah 14:12, which the King James Bible renders "How art though fallen from heaven, O Lucifer, son of the morning!" This has sparked some controversy, because "Lucifer" is equated with Satan. But this is one of those over-reactions to the King James rendering. The translators used "Lucifer" in its Latin sense of "Light-bringer," which is a fair rendering of the Hebrew word which means something like "one who brightens." Modern versions render the Hebrew word something like "Day Star"; it's thought by some to be a reference to the pretensions of the Kings of Babylon.
I'm a bit leery of this whole interpretation anyway. The idea of "Children of Light" or "Children of the Morning" is a common one in mythology, and might just have occurred to the author (whether Heber or someone else) because it sounds good.
Bradley cites Routley to the effect that 19 different tunes have been used for this set of lyrics. - RBW