It is believed that Bach composed either four or five passions. However, only two of those survived till nowadays – St. John and St. Matthew. Both of these music works set on the sacred Bible texts tell the story of Crucifixion of Jesus Christ and are performed on "Good Friday".
Despite that, they quite differ in style and character. Unlike St. John, St. Matthew Passion is rather a ‘religious opera’, it’s much longer (twice as many verses), more dramatic and action-oriented. It also has more music grandeur – with its 2-part choirs (each showing different crowds during the crucifixion) and a large orchestra that perfectly produces the dramatic effects (halo though strings ensemble, Christ’s weariness at Calvary though deep pedaling). The Passion was first heard on Good Friday of 1727 in Leipzig but was revised a couple of times after that.
Regardless of the work’s length it is worth listening to it from beginning to end – that’s the best way it’s perceived to the fullest. However, there a number of arias that are often taken as excerpts and make good separate music works. One of them definitely is the "Erbarme dich, mein Gott'" alto aria that, along with others, is based on Christian Picander’s texts. It describes Peter’s lament for having ‘betrayed’ Jesus three times before dawn and is extremely emotional. There also exists an interesting version as far as this aria is concerned. They say that Bach was inspired by love for his wife Anna Magdalena for composing this particular part of St. Matthew’s Passion and kinda ‘dedicated’ it to her. Well, who knows.
Meanwhile, have a listen to the aria itself and the bright counter tenor Peter Kenny singing it at the dramatization by Jonathon Miller: