It is a Christmas piece based on a Latin poem of the same name, which translates as "Light, warm and heavy as pure gold, and the angels sing softly to the new born babe".

[3] The poem is attributed to Edward Esch, described by Whitacre as "a recluse, in the truest sense of the word … born sometime in the early '70s, but rarely making a public appearance".

[7] In 2005, Whitacre adapted it for wind band, a version first performed at the annual conference of the Texas Music Educators Association and dedicated to Gary Green.

[9] The video as a mix of individual recordings by 185 singers from 12 countries caused "a colossal on-line rush in interest" when it was uploaded in 2011.

[12] Whitacre used the two initial chords of the conclusion of Passio by Estonian composer Arvo Pärt (Qui passus es) for the final word natum (new-born) and thus linking birth and death of Christ to reincarnation.