Thomas Braatz wrote (October 13, 2002):
BWV 48 - Some Commentaries:
The Only Real Dance in this Cantata [despite the fact that most HIP conductors want to make the arias into fast-moving dances]:
Surprise! The only bona fide dance mvt. in this cantata is the 1st mvt.!
In their book, “Dance and the Music of J. S. Bach” [Expanded Edition] by Meredith Little and Natalie Jenne, the authors give the opening bars of mvt. 1 as an example of a sarabande-like mvt. and state: In BWV 48,1, “counterpoint soon overcomes the four- and eight-measure sarabande phrases with which the piece begins. [The example] shows the impassioned cry of the troubled soul, in the long canonic lines in the soprano and alto parts, while the balanced phrases of the traditional chorale “Herr Jesus Christ, ich schrei zu dir” is heard in another canon above.”
On Naming that Tune:
Martin Petzoldt in volume 3 of the books accompanying the Koopman cantata series  (never fully translated into English as far as I know: “Die Welt der Bach Kantaten” edited by Wolff & Koopman) describes a feature that we encounter in mvt. 1 of this cantata: [paraphrase follows] In some cantatas we find the chorale melodies played by instruments, an important theologically structural factor because lurking behind such a compositional device is a kind of theological riddle or guessing game: “Can you name that tune?” “Can you relate the text of the chorale with the words being sung concomitantly by the choir?” “If you made the connection, then contemplate why this association is being made!” Bach used this technique as early as in his Weimar cantatas, but in Leipzig he seems to have thought about using this technique in various ways that he had never considered before. For example, in BWV 77/1, he introduces the chorale “Dies sind die heiligen zehn Gebot” [“These are the 10 commandments”] in a two-part canon in augmentation so as to remind the listener about the other, ‘second’ commandment of love. Other examples are BWV 23/2, BWV 25/1, BWV 48/1 [this cantata], BWV 70/9, and BWV 19/5. From the Weimar period we find BWV 185/1, BWV 163/5, BWV 31/8, and BWV 12/6.
The ‘Fatal Separation of Body and Soul’:
In his book, “Tonal Allegory in the Vocal Music of J. S. Bach,” Eric Chafe, probably because Bach left us no information about these matter, refers to Mattheson’s theories and gives us a very interesting example from this cantata that should shed some light on this very interesting subject. For this, listen carefully to what happens on the word, “Gift” [“poison”] in mvt. 2 (alto recitative.) This is the point of fatal separation between body and soul. I will quote Chafe directly:
“In Bach’s time the word [‘durus’] was increasingly used to mean major, although … the older usages – often suggesting hardness or harshness – had by no means disappeared. Mattheson acknowledged an association of sharp key signatures with the qualities of hardness, freshness, and gaiety but took pains to deny that such ideas could be used to explain the affect of any key. Nevertheless, he believed in the reality of key characteristics, at least in his earlier writings, and his famous characterization of the keys confirms the traditional associations in a number of respects. Significant for Bach’s usage is his calling E major expressive of “a quite deathly sadness full of doubt, most convenient for ‘extreme’ enamorment of helpless and hopeless things, and it has in certain situations such a cutting, separating, suffering, and penetrating quality that it can be compared with nothing but a fatal separation of body and soul.” Although it would be a serious mistake to apply such a description too literally, behind Mattheson’s rather surprising characterization we can see the ancient linking of sharps to the ‘cantus durus’ and of other deeper sharps to the idea of tonal extremes. Bach’s use of E major throughout the cantatas has, in the main, a positive set of associations, but it is still close to the idea of an extreme, and a key such a G sharp minor that is generally linked to pejorative associations sometimes appears in company with E major. Also, in a very few instances in Bach’s work E major is associated with anything but positive ideas; and in these cases it is possible that Bach reverted to something closer to Mattheson’s view.
Sometimes the confrontation of extreme sharps and flats suggests the idea of a “separation of body and soul.” Such an instance is the first recitative of Cantata 48, “Ich elender Mensch, wer wird mich erlösen.” Beginning in E flat, it modulates through F minor, C minor, and A flat to cadence in B flat minor for “Die Welt wird mir ein Siech’ und Sterbehaus, der Leib muß seine Plagen bis zu dem Grab mit sich tragen.” Then, on „Allein, die Seele fühlet das stärkste Gift, damit sie angestecket“ Bach makes a shift, via the enharmonic reinterpretation of several tones, to E major (or F flat). Here torment both of body and soul are confronted, a context that suggests the extreme character of E major.“