Catholic Encyclopedia (1913)/Verbum Supernum Prodiens
The first line of two hymns celebrating respectively the Nativity of Christ and the Institution of the Holy Eucharist. The hymnologist Daniel remarks on the obvious relation between the Nativity and the Eucharist "by which through all ages the Word made Flesh will dwell among us" as justifying the similar forms of the two hymns (Thesaurus, I, 254).
The Nativity Hymn
In its unrevised form the second line was: "A Patre olim exiens". The correctors of the Breviary under Urban VIII changed it into its present Breviary form: "E Patris aeterni sinu". Sometimes ascribed to St. Ambrose or to St. Gregory the Great, its authorship is unknown. Mone supposed it to be of the second half of the fifth century; but although Advent may possibly date back that far, the hymn is probably much later. From the tenth century it has been the usual hymn for Matins, although given in a few manuscripts to Lauds. Originally the hymn was rhymed throughout in couplets (with one exception). The revision under Urban VIII left not a single strophe unchanged, in the removal of its many unclassical prosodic features.
The Eucharist Hymn
Its second line is: "Nec Patris linquens dexteram". Left untouched by the revisers of Urban VIII, it lacks classical prosody, is in accentual rhythm, and rhymes alternately:
Verbum supernum prodiens
Nec Patris linquens dexteram,
Ad opus suum exiens
Venit ad vitae vesperam.
The Word of God proceeding forth
Yet leaving not the Father's side,
And going to His work on earth,
Had reached at length life's eventide.
The hymn is assigned to Lauds of Corpus Christi (q.v.) and is commonly ascribed to St. Thomas Aquinas. Some scholars compare the Office of Corpus Christi with that of the older Cistercian breviaries (1484-1674), and suggest that St. Thomas probably borrowed (while revising) seven of the responsories of Matins from it, and also probably the hymn "Verbum Supernum". In the Cistercian Office the hymn comprised nine stanzas divided into two hymns (for Matins and Lauds respectively), whereas now the hymn has only six stanzas. The Cistercian hymn was sung to the melody of the Advent hymn, "Verbum Supernum", whereas we now sing the Eucharistic hymn to the different melody of the Ascensiontide hymn, "Aeterne Rex Altissime". "It is very natural to suppose that this choice (a common melody, as in the Cistercian Office, for both of the Verbum Supernum hymns) was the primitive one" (Morin).