The text is by Patrick Wilkinson, and is a Latin version of the Parable of the Good Samaritan (Luke 10:30).
The work is scored for tenor and baritone soloists, mixed choir and string orchestra with piano, harp, timpani, and a string quartet.
The string quartet represents time passing, and once again someone is seen approaching. Similar hope is expressed by the chorus, and the tenor pleas for help, but the Levite continues on his way.
After the passage of time, the Samaritan appears in the distance. The chorus acknowledges his arrival, it is not with the hope that they previously showed. They ask him why he would want to stop and help a Jew. As the Samaritan stoops to help, though, the tenor's feeble cry for help becomes a soaring arioso. They chorus joins in a triumphant C-major theme reminiscent of Stravinsky, and the tenor and baritone sing D-major duet.
In the epilogue, the tenor and baritone sing that they now know who their neighbour is. The chorus recapitulates the prologue, singing "Go and do likewise."
The Cantata Misericordium is considered by many to be an epilogue to the War Requiem. Some critics feel that it has less of an impact, however, due to the somewhat dull Latin text. Since the piece was written for an international event, Britten probably felt that English text would be inappropriate.