Here are two recordings of the Alto Aria Erbarme dich from J.S. Bach’s St. Matthew Passion, followed by a recording of the entire Passion, which in turn is followed by a recording of Bach’s St. John Passion.  No words of description are needed.  Just start listening, and you will be swept up in the Passion.  The Aria in the first two recordings takes place as the cock has just crowed and Peter realizes that he has denied Jesus three times, as Jesus foretold.