G sharp minor isn't a friendly key to play in at the best of times. With its four sharps and a double-sharp, it's the musical equivalent of picking over barbed wire. In Bach's day, it would have been even more painful. The tuning systems that were used made nice friendly keys like C major and G major sound even more rich and in tune than they do today. But the pay-back was that if you played in remote keys with more than a few sharps and flats, the effect was unnerving at best- and at worst like having pins driven into your forehead. This necessarily wasn't considered a bad thing. Bach's generation liked to keep the characters of the individual keys, without smoothing them all out like modern tuning systems (A much more technical explanation of this is at http://en.wikipedia.org/wiki/Well_temperament) . And so when you hear a sudden chord of G sharp minor played on instruments of Bach's time, it shoots right through you.
And unbalanced discord shooting through harmonious relationship is precisely what this week's cantata is all about. It all starts off very solidly and almost pompously. A stately opening chorus, with fanfare-like interjections for the “Friedefürst”- the Prince of Peace- ends with a solid, confident declaration: “D'rum wir allein in Namen dein Zu deinen Vater schreien”. It's a common enough sentiment in Lutheran theology: only through Jesus' name do we call to the Father. And the word “schreien” resolves downwards in a confident A major chord.
But the second movement tears this apart- it's a direct criticism of the first movement's confidence. We start with the repeated word “Ach!” from the alto. “Ach” is a remarkable word. It's not just a cry of pain, despite the resemblance to “ouch” in English; it literally means pain. The only words that the singer can express are “pain, pain, pain”. Bach's vision is terrifying. This is the cry we make to the Father through Jesus: not confident Lutheran foursquare chorale singing, but weeping with pain. When we finally get to some more actual words in the rest of the line, ironically they can only emphasise the inarticulacy of the tormented soul: “Unaussprechlich ist die Not”: the agony is indescribable, and all that can be expressed is agony itself.
Here is the alto's “Ach!”. Instead of a solid, falling resolution like at the end of the first movement, it rises up, un-grounded and uncertain:
Du Friedefürst, second movement, bars 11-15
And if we look more closely, we see it's sung to two jagged fragments of the movement's opening melody. It's almost as if the singer is too overwhelmed with the pain to complete the lyrical line- a musical depiction of angst that is unaussprechlich, fear of sin combining with fear of God to break the song into pieces.
Du Friedefürst, second movement, bars 1-4 (keyboard reduction)
With the third movement's brief recitative link for the tenor, we begin the fourth movement with an unsettling thought: we can scarcely cry to the Father through Christ if he turns away from us. But here we are taken from uncertainty into a new sublime sound-world, one very rare even for Bach: a terzett or trio of voices, the soprano, tenor and basses weaving round each other hypnotically. Only the yearning of the cello underneath reminds us of the pain of the previous movement, as the three voices repeat the phrase “wir bekennen unsre Schuld, wir bekennen” again and again- “we confess our guilt, we confess”; and there's a lovely thinning of the textures as the voices sing “wir... bitten nichts als um Geduld”- we ask for nothing but patience.
Yet the outside world crashes back in. The next alto ario takes us from E major to F sharp minor, and then on the words “die scharfen Ruthen”- the harsh rod- we have a chord of the dreaded G sharp minor (with an added F sharp for extra spice):
It's the very edge of usability in the tuning system that Bach would have used. And although we return to a more tuneful A major by the end of the recitative to lead into a muted chorale, the cantata as a whole still seems a strange and unsettled.
What is going on? Well, one suggestion is that Bach isn't only on the edge of tuneful harmony in the music. In the words, he and his librettist are flirting with a controversial theological doctrine that some people think is on the edge of heresy. The key words are in the wonderful serene trio: “Es brach ja dein erbarmend Herz, Als der Gefallnen Schmerz Dich zu uns in die Welt getrieben”. “Your merciful heart yielded, for the pain of the fallen drove you to us in the world.”. This is actually dangerous stuff; it suggests that within the eternal and unsuffering Trinity, the pain of a fallen world reached all the way up to the Godhead. It may be heretical, but it explains why at the heart of this cantata there is a moment of stillness- a trinity of voices, dancing round each other- which is suddenly interrupted when we are thrown back to a world of pain. Bach's music follows the journey of God's Son to a world of anguish. And it's appropriate that in journeying from heavenly harmony to the moment of the deepest earthly discord, we reach a key with four sharps and a double-sharp. For the German word for a sharp is kreuz- a cross. Only there do we see the Friedefürst, the prince of peace.