Gregorian chant is distinguished by a certain Roman economy, scarcely ever repeating a text, except in the case of litanies. There are several offertories, though, which make repetitions within their texts, and they often occasion the question, why? In considering their texts, it is clear that these repetitions are for a variety of reasons.
Perhaps the most interesting repetition occurs in a pair of offertories, both beginning "Jubilate Deo," the first in mode five, the second, in mode one. (1) These two chants, though their texts come from different psalms, (2) take their main point of departure from their first two words, which they have in common: the injunction to sing joyfully, to jubilate. Their placement on consecutive Sundays suggests not only the joyful character of the Epiphany season, but also that their direct comparison is invited.
The musical injunction, "Jubilate Deo," forms the topic of the beginning of both chants, for musically speaking it is more specific than simply "sing joyfully"; rather, the joyful singing is accomplished through a jubilus, a long melismatic passage on a single syllable. Thus, the response to the injunction, "Jubilate" is a repeat of the text in which the jubilus occurs upon its accented syllable. In each chant this melisma is made more beautiful by its own internal organization. Each makes it clear that its repeat of the first word is anything but a simple melodic repeat.
In the first, Jubilate Deo omnis terra (Ex. 1), the initial intonation Jubilate rises to a c and then descends to center around F and G. (3) The repeat Jubilate then projects a melisma that clearly sets off in a new direction, creating a series of segments, varying the third, a-c:
1) a-c emphasizes c, falling briefly through a to F;
2) a-c is recovered, adding another third, c-e;
3) a-c-e now turns slightly downward, leading to
4) an alternate third b-flat to G leads downward to F, but then a-c-e is recovered, as in #2
5) a-c leads back down to F, leading in turn to "Deo: repeated exactly as in the initial intonation.
Each of these motivic segments develops an idea from the previous one, creating a coherent whole that amounts to a kind of progressive variation.
The second, Jubilate Deo universa terra (Ex. 2), begins with a formulaic mode-one intonation and leads to a musical colon, cadencing on what amounts to a kind of half-cadence on "universa terra," that indicates that something more is to come. The melisma which follows is quite different from that of the previous piece: it forms one very large melodic gesture that reaches a peak and resolves to "Deo," reiterating that word exactly from the intonation. The stages are:
1) beginning on a it adds a c above, only to plummet to the C an octave below;
2) that C alternates with double notes (bistropha) on D then on F, then on a;
3) then it becomes triple notes (tristropha) on a then c, with a bistropha on d;
4) it rises finally through e to an f above, the peak, turning back to c and then a.
The overall shape of this melisma is a large arch, whose beauty is its breadth and scope, comprising a range of an octave and a fourth.
Both of these chants, in musically quite different ways, respond to the imperative "jubilate," by jubilating, singing a jubilus. Incidentally, both complete chants comprise two psalm verses, each consisting of two complete statements. These statements are strikingly distinguished from the verse of the melisma musically, in the first by a shift of emphasis upon B-flat to B-natural, and in the second by a gradual ascent and descent, which helps to create the overall shape of the piece, as well as a remarkable repose at its end. The mode-one Jubilate is one of the longer offertories of the year, one which must have been very well liked, for it is repeated on another Sunday, in the Easter season. …