Articulation
Bach's working method was enturely geared to the performance in hand, with the result that his scores contain few indications of the way in which he intended them to be articulated. Normally, the full score reflects the overall picture of the piece, whereas the orchestral parts, which were written for the musicians and used by them at the performances superintended by Bach, contain detailed performance markings. An exception to this is Part Six. Here Bach reused some of the parts from his lost Cantata 248a, namely, the second parts of Violins I and II and the continuo, together with the organ part. Could the differences between the parts and the full score indicate that in this special case the full score should be regarded as the definitive version of the finisched work? In no. 54, for example, some of the parts include dots over each quaver, notably in bars 17-20 and 113-16, whereas the full score has slurs over two or three quavers in each bar. But this cantata contains so many different layers of corrections and revisions to those corrections (some parts were evidently written out only after the full score of the Christmas Oratorio was completed, then corrected by another copyist in the light of the older cantata parts and then corrected a second time by a firther copyist, possibly Bach himself) that it is very difficult to establish a definitive reading.
The question of articulation is less problematical in the other parts of the oratorio inasmuch as fewer layers are involved. Here all parts were specially prepared for the performances of the work supervised by Bach, who corrected most of them himself, with the result that the original performing material is relatively accurate. even so, it was necessary to add a whole series of articulation slurs that were presumably so self-evident to the musicians of Bach's own day that he simply did not need to include them. Time and again one is struck by the fact that even when the writing for the instruments is colla voce, Bach did not intend their articulation to mirror the syllabic division of the words in the choruses, while preludes that share the same themes as the vocal passages that follow are often articulated in very different ways. Examples include nos. 4, 19, 21 (from bar 31), 36 (from bar 97), 39, 47 and so on. (This is a recurrent problem in Bach's cantatas, oratorios and Masses, noticeably so in the inner voices in the chorales.) The articulation markings in the full score are frequently different fron those in the parts, and may even differ in parts where the  writing is otherwise parallel. There are several possible reasons for this. In every case we chose the interpretation that seemed to us the most convincing, and in the light of this decision we aligned all the other parts with it. The complex interrelationship of lenght, brevity, stress and ties or slurs was evidently so important for Bach that he scratched out or erased a number of passages, correcting and clarifying even such apparently unimportant differences as          and       . In doing so, he distinguished between three different stages:       ,             and     . He also added dots and vertical strokes, the meaning of which varies from instance to instance in keeping with the context and with Baroque practice in general. The most frequent meaning is no doubt a sforzato-like emphasis, the strict Baroque hierarchy of "strong" and "weak" beats that normally needs to be heeded in  determining the corrent articulation - 4/8         (1 strongest, 3 less strong, 2 weak and 4 weakest) - being cancelled out by the dots.          would therefore be executed as four notes all bearing equal stress. (Dots are found, for example, in the violin part in no. 31.) The dot is also occasionally found as an indication that the note should be shortened. If it occurs at the start of a slur, as it does over the semiquavers in no. 54 ("Herr, wenn die stolzen Feinde schnauben"), the accentual character is particularly striking. The term "spiccato" or "staccato" that Bach uses relatively frequently has nothing to do with its modern technical meaning but refers simply to the fact that the notes should be clearly separated. A typical example of this comes in no. 57. "Nur ein Wink von sienen Händen", which is marked "Largo e staccato".

Instrumentation
Each of the six parts of the Christmas Oratorio is so characteristically orchestrated that its sound picture invariably allows the listener to "see" the desired scene. Part One is filled entirely with a sense of jubilation at the coming of Christ as ruler. There is no trace here of any saccharine sentimentality. The final chorale sets up a link with the following scene involving the shepherds. Here there are three levels to the sounds that we hear: (1) the chorale in its usual simple instrumentation, with flutes at the upper octave adding a brighter sound to this delightful tribute to the Infant Jesus; and (2) the third trumpet and timpani, wich express the traditional Baroque affect of majesty and which (3) enter into dialogue with the first and second trumpets, the writing for which is cantabile and not al all heroic. The impression is that of the skies opening above the manger. The sonorities of Part Two are entirely geared to the portrait of the shepherds, and here the sound picture is dominated by the choir of oboes. Even the angelic host is incorporated into this pastoral scene. In Part Three we find a further stark contrast with the previous cantata. Here the earztly joys of the shepherds are transformed into a magnificent homage to the Son of God by means of trumpets and timpani, the instruments associated with royal rule. As a result, the direct link between these two scenes invelves a complete change of affect, producing two views of the same event frem altogeter different perspectives. The shephers are shown as representatives of the whole of humanity, their shepherd-like characteristics receiving no further mention. Following the wonderful scene with the Virgin Mary and the return of the shepherds to their fields, the jubilant opening chorus is repeated, the initial image reinforced by all that has happened in the meantime. Part Four is in F major and occupies the middle ground between the Baroque jubilation of the two cantatas in D major and the pastoral cantata in G major. It describes the circumcision and naming of Jesus. Soft-grained natural horns gives this part a meltingly lyrical tonal picture that constitutes a tribute to the name "Jesus". At the heart pf Part Four is the chorale "Jesu, du mein liebstes Leben" (38 and 40), which is based on a melody pf Bach's own invention. Like no. 7 in Part One ("Er ist auf Erden kommen arm"), this chorale was described by Bach as an "arioso," a term no doubt used to explain the presence of a soloist. In both cases the bass soloist provides a touching commentary on the message of faith contained within the chorale, the soloist standing in for mankind, the chorale representing the Church. Part Five describes the search of the Three Wise Men for the Infant Jesus. It was no doubt for dramaturgical reasons and out of regard for the key structure of the work as a whole that Bach dispensed with the D major brilliance of the trumpets here. This part is in A major, the dominant of the D major of Part Six. The oboes d'amore are in A and therefore play in C, producing a relatively bright and resplendent tone for so soft-grained and gentle an instrument. They are used in the opening chorus (43) as equal partners in a dialogue with the choir, while the strings depict humanity's bustling sense of joy. With its solo writing for the oboe d'amore, the bass aria (47) dispenses with the continuo instrument - cello or bassoon - that one normally finds in such a movement. The corresponding orchestral part contains the performance marking "tacet" at this point.
The organ part is also given a more obbligato role to play than in the other arias. Above all, the writing is more clavier-like, so that the part lies awkwardly for an accompanying instrument. The trio (51)is one of the dialogues between the daughter of Zion (soprano and yenor) and the soul of the believer (alto) that were popular at this period. Part Six shows Christ as victor and avenger: when protected by Him, the faithful have nothing to fear. Here D major and the sound of victorious trumpets are self-evident. In stark contrast is the opening chorus of Part Six (54), into which Bach introduces bars of trembling semiquavers marked piano over dissonant harmonies, perhaps intended to depict our fearful hesitation before the trust and courage described later in the chorus reassert themselves (see, especially, bars 20-23, 44-7, 116-19 and 212-15). Bach repeatedly altered the instrumentation of this movement febore finally giving the first trumpet a sustained note, while the second and third trumpet and the timpani are silent. All of them enter again with the forte entry in bar 23 and later. Perhaps this held note is intended to portray the trust that remains unbroken even in fear. On the fifth and final appearance of this passage in the fifth bar from the end, the chorus dispels all misgibings with its forte interjection at the words "nach deiner Macht" ("to Thy might").
There are many points in the full score of the Christmas Oratorio where the precise instrumentation has not been entered, so that it can be deduced only from the parts. The same is true of the use of particular instruments, notably the oboes. Bach often writes "Hautbois" even when he means oboe d'amore. The oboists of the period were no doubt used to taking up whichever instrument was appropriate to the key of any given passage even when it was not specifically indicated. (Much the same is true of the oboe parts in a number of Bach's cantatas.) Sometimes the player must have had to change his instrument sooner than is indicated in the part or continue to play on the new instrument after the change. In Part One, the instruments in question are initially oboes, but in no. 3, the players switch to boes d'amore, sticking with these instruments throughout the rest of Part One. In Part Three, oboes are used initially, but oboes d'amore take over in the first chorale (28) as the players can no longer change instruments before the aria. They then change back to oboes for the rest of Part Three. Part Six begins with oboes, but oboes d'amore take over in no.59 in order to be ready for the accompanied recitative (61). After no. 62 they revert to ordinary oboes. In the majority of cases neither the full score nor the orchestral parts allow us to decide definitively which continuo instruments are to be used in individual arias and recitatives, so that the interpreter has to decide each case in turn, taking account above all of technical and acoustic considerations.