Ich lasse dich nicht, du segnest mich denn, BWV 157

 (I will not let you go, except you bless me), BWV157, is a church cantata by Johann Sebastian Bach. He composed it in Leipzig in 1726/27 to a libretto by Picander. The first known performance was on 6 February 1727 in a memorial service for Johann Christoph von Ponickau in Pomßen near Leipzig. The work was later assigned to the feast of the Purification on 2 February.
Picander included a quotation from in the first movement, and the last stanza of Christian Keymann's "" in the closing chorale. The contemplation begins with the Old Testament quotation being applied to Jesus, and leads to the last aria expressing an eager wish for death to arrive soon. The closing chorale picks up the first line.
Bach structured the cantata in five movements, scored for two vocal soloists, tenor and bass, a four-part choir, and a Baroque instrumental ensemble of flauto traverso, oboe d'amore and continuo in the original version as reconstructed by Klaus Hofmann. In the later version, there are parts also for oboe, two violins and violetta. 
History and text.
The work appears to have been commissioned as a funeral cantata for Johann Christoph von Ponickau (1652–1726), a Saxon chamberlain. Picander, Bach's librettist, clearly linked the cantata to Ponickau, publishing an extended funeral ode on his death, followed by the text of the cantata. The first known performance was at a memorial service for Ponickau on 6 February 1727 in the church of his home village, Pomßen (20 km from Leipzig). The event is quite well documented in that there a printed commemoration sermon giving some information about the music performed, which included a second Bach cantata, the now lost "Liebster Gott, vergißt du mich", BWV Anh. 209. That work was written to a libretto published by Georg Christian Lehms in his "Gottgefälliges Kirchenopfer" for the seventh Sunday after Trinity.
For "", Picander included a quotation from in the first movement, but the line from Jacob wrestling with the angel is understood as a believer addressing Jesus. The closing chorale is the last stanza of Christian Keymann's "".
The cantata appears to have been adapted for performance as part of Leipzig's church music, specifically for the Feast of the Purification of Mary which was celebrated on 2 February. The existence of more than one version is implied in the earliest surviving manuscripts, from after Bach's death, copied by Christian Friedrich Penzel. The primary surviving score dates from 1755 and there are parts from the 1760s. The prescribed readings for the feast day were from the book of Malachi, "the Lord will come to his temple" (), and from the Gospel of Luke, the purification of Mary and the Presentation of Jesus at the Temple, including Simeon's canticle Nunc dimittis (). The idea from Simeon's canticle to depart in peace has often been used as an image for the death of a Christian.
Scoring and structure.
Bach structured the cantata in five movements. He scored it for two vocal soloists, tenor (T) and bass (B)), a four-part choir only in the closing chorale, and a Baroque instrumental ensemble. According to the 1760 set pf parts, he scored it for flauto traverso (Ft), oboe (Ob), oboe d'amore (Oa), two violin parts (Vl), violetta (Vt) and basso continuo. Hofmann derived a version from the 1755 score for a smaller ensemble of flauto traverso, oboe and viola d'amore which may have been closer to the one used for the first performance. The duration of the cantata is given as 21 minutes.
In the following table of the movements, the scoring, keys and time signatures are taken from Dürr. The continuo, which plays throughout, is not shown.
Music.
The music of the original version has been described as chamber music by Klaus Hofmann, using "an exquisite combination of solo instruments".
The opening movement sets only a single line: the biblical quotation from Genesis which became the title of the cantata: "" (I will not let you go, except you bless me).. The movement has an eight-measure ritornello that opens, ends, and bisects the movement; it features a prominent imitative motif. The two solo voices sing the theme, which was introduced by the continuo, in a canon.
The second movement, "" (I hold my Jesus tightly), is a tenor aria accompanied by continuo and obbligato oboe d'amore, which perform a long ritornello serving much the same structural function as in the first movement. Craig Smith suggests that this is "perhaps the single most difficult tenor aria in the whole repertoire", with "wild and extremely ornate melismas".
The tenor recitative, "" (My dear Jesus, when I suffer oppression and torment, then You are my joy), is accompanied by strings. It recalls some of the motivic material from the first movement.
The fourth movement, for bass, "" (Yes, yes, I hold Jesus tightly, therefore I will also enter into heaven), combines elements of aria, recitative, and arioso. It opens with a ritornello of violin, flute and continuo. Structurally, the movement completes most of a da capo aria before a recitative episode interrupts the reprise of the A section. The music moves between aria and recitative twice more before a final aria section ends the movement.
The cantata ends with a four-part setting of the chorale, "" (I will not let go of my Jesus, I will walk beside Him forever) with a conjunct melody and active continuo line. The last line is the same as the first, connecting to the beginning of the cantata.
Recordings.
Recordings of include: