Musically Bach goes to town with this phrase and sets the final three words highly effectively, not once, but twice, with agonising syncopation and extreme tortuous, twisting chromaticism. The jagged and illogical harmonic progression of the passage, and the rhythmic movement of the words describing Peter’s distress being largely syncopated with the uncharacteristically consistent beat provided by the continuo, symbolise the fact that Peter is so at odds with himself. Note also that the bass line, which has been chromatically rising, starts to descend (or retreat) as soon as the word bitterlich is used.

Musical Fragment und weinete bitterliche










Und Hannas sandte ihn gebunden zu dem Hohenpriester Kaiphas. Simon Petrus stund und wärmete sich, da sprachen sie zu ihm:







Now Annas had sent him bound unto Caiaphas the High Priest. And Simon Peter stood and warmed himself. They said therefore unto him:






17 Chorus “Bist du nicht seiner Jünger einer?” “Art not thou also one of his disciples?”
18 Evangelist Er leugnete aber und sprach: He denied it and said:
  Peter  “Ich bins nicht.” “I am not.”
  Evangelist Spricht des Hohenpriesters Knecht’ einer, ein Gefreundter des, dem Petrus das Ohr abgehauen hatte: One of the servants of the High Priest, being his kinsman, whose ear Peter cut off, saith:
  Servant “Sahe ich dich nicht im Garten bei ihm?” “Did not I see thee in the garden with him?” 
  Evangelist Da verleugnete Petrus abermal, und alsobald krähete der Hahn. Da gedachte Petrus an die Worte Jesu und ging hinaus und weinete bitterlich. Peter denied again and immediately the cock crew. And Peter remembered the word of Jesus, and he went out and wept bitterly.