In 1735, only months after the composition of the six cantatas that comprise the Christmas Oratorio, Bach finished yet another oratorio-like work, the Ascension Oratorio. Although the readings assigned to the day in the lectionary are the end of the Gospel of Mark and the very beginning of Acts, Bach also draws upon the account in the 24th chapter of Luke. All of the concerted music except for the two chorale settings was arrangements of music from previous secular works. Like all of the music in the Christmas Oratorio, these arrangements are of such a high order and are so skilled that one has no sense of any inappropriateness of the music.The Oratorio begins with a bright and brilliant chorus in D Major with not only flutes and oboes but also trumpets and drums. The work is propelled along by a memorable theme in the trumpets. The schleifers in the 3rd and 4th bars are particularly riveting and help us keep our place in the phrase throughout the movement. There is something simple and artless about this da capo chorus. It is in a way the Bach trumpet and drum chorus sui generis. Its materials are so simple that one could think that it is generic, except that it keeps one's attention riveted from beginning to end. The middle section has a jaunty little syncopated figure that not only enlivens the texture but comes back at the very end of the oratorio to remind us from where we've come.The evangelist, like all of Bach's Evangelists, a tenor, is perhaps a little more sedate than either the Christmas Oratorio or the Passions. The accompanied recitatives are both accompanied by a pair of flutes, emphasizing the calm almost pastoral character of the piece.
The first aria, #4 for alto and unison violins, is much better known in its later version as the Agnus Dei from the B Minor Mass. The German words here are particularly suited to the line. The Mass version is virtually identical in the violin and continuo parts but quite changed in the voice part. Here the voice sings the theme as played by the violins. In the mass the voice sings, rather seraphically, a countermelody. The two versions have such a different function in their respective pieces that it is futile to compare their virtues. The music qua music is of the highest quality and the heartbreaking sadness of the melody brings an interesting touch to this story, which is on the surface a happy one. After the opening it is interesting that the Ascension Oratorio in both its arias and recitatives is bathed in melancholy. Another brief narrative fragment of the Evangelist brings us to the middle of the work a setting of the chorale “Ermuntre dich, mein schwacher Geist.” The melody is pitched unusually low, as if all of us who remain behind are literally at Jesus' feet.
The narration begins again, this time, the episode from Acts, which tells of the two men in white garments who ask why we are amazed at what is happening. The bass joins the tenor for an extended duet arioso on these words. This leads into a brief accompanied recitative for alto and again, flutes commenting on the situation. The Evangelist then returns describing the disciples return to Jerusalem.The next aria, #8 for soprano, flutes, oboe and the upper strings playing the bass line, is one of the most mysterious and beautiful things in the oratorio. Clearly drawing upon the line of text “Kann ich doch beständig sehn. Deine Liebe bleibt zurücke” for its affect, the work is bathed in the glow of the “love left behind.” The lack of bass gives the piece a floating quality and also obviously refers to Jesus floating in the air. What is perhaps more interesting is the complex continual forward motion. The piece doesn't really divide up into phrases but is rather one continuous and somewhat unarticulated line. The 3/8 time and the three voices (flutes, oboe, soprano) may be symbolic of the Trinity, for clearly the text is heavily Trinitarian. That is probably less important than the stopped time quality of the piece which is quite hypnotic.
The final chorale is an amazing tour de force. A verse set to the melody of the grave chorale, ”Von Gott will ich nicht lassen,” is imbedded in the brilliant trumpet and drum dominated D Major texture of the orchestra. The B minor of the chorale never loses its identity but is simply swallowed up in the D Major. Bach understands the melancholy of being left behind, and profoundly includes it here in this ostensibly joyous festival. The little syncopations of the opening chorus here dominate the rhythmic motion giving the piece a kind of curious and again psychologically complex urgency. It is interesting that here near the end of Bach's career of writing every-day liturgical music, he writes a piece so stunningly honest and full of insight, while reusing much of the time secular materials that on the surface seem inappropriate.