Gloria in excelsis Deo was written in Leipzig for Christmas Day, as indicated by the heading on the manuscript in Bach's own handwriting, "J.J. Festo Nativit: Xsti.", to be sung around the sermon. Recent archival and manuscript evidence suggest the cantata was first performed, not in 1743, nor in 1745 at a special Christmas Day service to celebrate the Peace of Dresden, which brought to an end the hardships imposed on the region by the Second Silesian War, but likely in 1742, for a regular Christmas celebration by the university of Leipzig at the Paulinerkirche. Unlike Bach's other church cantatas, the words are not in German, taken from the Bible, a chorale or contemporary poetry, but in Latin, taken from the Gloria and the Doxology. This late work is the only Latin cantata among around 200 surviving sacred cantatas in German. It is based on an earlier composition, Bach's 1733 Mass for the Dresden court, which would, in 1748, become the first part of his monumental Mass in B minor. The first movement is an almost identical copy of the first two movements of the Gloria of the earlier work, while the second and third movements are close parodies of the earlier Gloria's fifth and ninth movements. Parts, for instance, of the fugal section of Sicut erat in principio, taken from the Mass in B minor structure#Cum sancto spiritu of the 1733 setting, are moved from a purely vocal to an instrumentally accompanied setting. The modifications Bach made to the last two movements of BWV 191, however, were not carried over into the final manuscript compilation of the Mass in B minor, leaving it a matter of speculation whether or not these constitute "improvements" to Bach's original score.
Scoring, words and structure
The cantata bears the heading ::J.J. Festo Nativit: Xsti. Gloria in excelsis Deo. à 5 Voci. 3 Trombe Tymp. 2 Trav 2 Hautb. 2 Violini Viola e Cont. Di J.S.B. in Bach's own handwriting. The cantata is festively scored for soprano and tenor soloists and an unusual five-part choir, three trumpets, timpani, two flauto traverso, two oboes, two violins, viola, and basso continuo. Its only link to Christmas is the opening chorus on Luke, to be performed before the sermon. The other two movements after the sermon divide the general words of the Doxology in a duet Gloria Patri et Filio et Spiritui sancto and a final chorus Sicut erat in principio. The final movement may contain ripieno markings similar to the ripieni found in Unser Mund sei voll Lachens, BWV 110, which was also a nativity cantata.
