A dark and imposing masterwork like the St. John Passion needs a moment of joyful reprieve. That reprieve comes in the form of the soprano aria ”Ich folge dir gleichfalls mit freudigen Schritten" (I too, follow you with joyful steps), in which we hear light flutes bouncing their steps. But even this happy sound comes with a strange chromatic ascent as the soloist sings "do not cease to push me, to pull me...". The St. John Passion is partly an instructive drama about how to follow Jesus; Peter must do his best at this despite his faults and denials. With this moment in this aria, we are dramatically pulled by Christ back into his own passion story.
St. John Passion: ”Ich folge dir gleichfalls” aria as performed by the Netherlands Bach Society: https://youtu.be/zMf9XDQBAaI?t=1315