This is the seventh of the ten movements of Camille Saint-Saëns' Oratorio de Noël, Op. 12, a piece that I'd never heard until the user Otterax suggested it to me on my Patreon page. This Oratorio has often been compared in terms of overall structure and inner passages with the typical sixteen century baroque oratorios of Händel and Bach because of its lyrical content (typical of their cantatas). Saint-Saëns' musical style has been described as elegant, well-balanced and clean, but this short piece, "Tecum Principium", also shows how the french composer used the advanced modern harmonic techniques of his time.
It is written for soprano, tenor, baritone, harp and organ, and begins with the two latter stating an introduction in G minor to the first motif, sung by the tenor, then by the soprano and finally by the baritone. The music then proceeds to develop this and another motif, while the harp makes beautiful arpeggios. Even though the piece starts with a very typical harmonic sequence, which also follows a normalized classical voice-leading procedure, the singers and the instruments begin to wander around when the second motif is presented. This divagation can even be considered as a non-functional harmonic passage because of the quick, forced modulations and the use of nondiatonic passing chords, but it nevertheless presents a clear magnific musical fluidity (just look at how the soprano descends chromatically from an F#5 to a B4 (cc. 21 to 27). The second part begins with the first motif but in the major mode, G major, and so the movement ends in this key.
Form and structure
Introduction (1-4) First part in G minor (5-29)
First motif and development (5-16): G minor, Bb major, Eb major
Second motif and development (17-29): "D major" (Non-functional harmony)
Second part in G major (30-56)
First motif and development (30-37): G major
Second motif and development (38-56): C major, Bb major, G major, F major, G major