Within its overall bipartite structure, the piece can be subdivided into numerous smaller sections, usually demarcated by changes of texture. As is standard in cantus firmus works, the tenor’s first entry is delayed, and following the vigorous opening, a low-voice duet lowers the temperature before the reappearance of superius and altus heralds the initial tenor entry (0'59"). The next significant occurrence is the series of leads at ‘subito’, recalling the equivalent excitement in Handel’s Messiah at the words ‘and suddenly there was with the angel …’. Following this section (2'30") the tenor drops out again and a sinuously winding duet and trio section proclaims the supremacy of the king of peace. The tenor re-enters at 3'31" and shortly thereafter a change of mensuration produces a rapid triple time (tempus perfectum diminutum) which completes the prima pars with a brief but joyous ‘Noël’.
The secunda pars is comparatively simple in its structure, being defined by a single if lengthy absence of the tenor. Following the opening ‘Puer natus est’, a brief duet (‘Verbum caro factum est’—‘The word was made flesh’) introduces a section of choral recitative (‘et vidimus gloriam eius’—‘and we saw his glory’). Brumel has been criticized for writing ‘mere recitation’ at times, but here the fluidity and suppleness of the homophony produces a beautiful effect, especially in the context of so substantial and at times frenetic a piece. Following this peaceful interlude, the energetic style returns with another triple-time subsection (‘Magnum nomen Domini Emanuel’—‘The great name of the Lord, Emmanuel’), before the tenor re-enters for a final time (6'44") as the mensuration returns to duple time (strictly speaking, it had never left, as the triple time was here achieved by coloration rather than by a separate mensuration sign as had been the case in the prima pars).
The final subsection gradually winds up the tension via a series of repeated descending phrases in the superius, each beginning a fifth above the final and cadencing on it; later (at 7'04") the formula is transposed up one tone and used in alternation with the original pitch. In the last few bars (7'38") a new rising phrase is substituted, which builds sequentially into the final ‘Noël’, which concludes with perhaps the longest false relation ever written, lasting a longa (four semibreves). The piece as a whole stands as a virtuosic demonstration of Brumel’s compositional technique, which juxtaposes radically differing styles and textures to create a glittering musical collage.
from notes by Stephen Rice © 2014