"Erlkönig" is a haunting and moving piece. Schubert is a master of text painting and once again proves that with this song. We all know the horse trotting sound that is produced by the bass line and the frantic chords in the right hand. But what everyone may not notice is the Neapolitan sixth chord in measure 143.
The N6 appears in the last half of the final verse. At this point, the Erl King has taken the boy away from his father and the boy is screaming for help as the King does him harm. The father rides swiftly with his son in his arms but by the time he stops riding, his child is dead. It is the father's arrival to the courtyard that brings about the N6 chord. It is proceeded by a iv chord, which is typical, and bring the verse to a sort of halt. It almost pauses the music, mimicking the father's distress and loss of hope for his son. The chord is not resolved immediately like the listener would expect, but is stretched out through the next couple of measures. This is Schubert's way of intensely painting the father's distress and the abrupt moment when he looks down and realizes his son is dead. It's the feeling of your heart stopping and your breath being taken away for what seems like forever when you realize something horrible has happened. Schubert physically writes in this pause with 4 beats worth of rests after the N6 chord on "Noth" in measure 145. He proceeds with the final recitative and brings the song to a close with the final i chord.
Even though this N6 may not be extremely noticeable at first, after a few hearings and reading the translation, it makes sense. A N6 chord is used to enhance the harmonic structure and overall tone of the melody its embellishing. Schubert uses his incredible text painting skills to place this unexpected chord at the end of the song to leave the listener with the lingering feeling of anguish and despair, thus connecting the audience with the father.