John Harbison does not take a hierarchical attitude to his music. The Pulitzer Prize-winning composer is glad when any of his works, however big or small, is performed. “I always tell my students, ‘Don’t take anything lightly,’” he said.

So in that spirit, he was thrilled to learn that musicians of the Chicago Symphony Orchestra will perform his Little Fantasy on The Twelve Days of Christmas (1988), a work for brass quintet that lasts just three minutes.

It will be performed in Episode 10 of CSO Sessions, a holiday-themed program that premieres Dec. 17 as part of the ongoing series of small-ensemble concerts streamed on CSOtv. Also featured will be Arcangelo Corelli’s Concerto grosso No. 8 (Christmas Concerto); J.S. Bach’s Brandenburg Concerto No. 2 and Gustav Holst’s In the Bleak Midwinter (arr. Higgins).

The piece came about in an unusual way. Harbison owed money to a law firm because of a chamber ensemble he was involved with, and he offered to pay off the debt with a short composition. The attorneys agreed and asked him to write something for their annual holiday cocktail party.

The result was the Little Fantasy, which the composer later incorporated into his Christmas Vespers, a work for brass quintet and narrator that incorporates text from the well-known nativity story in Matthew’s gospel.

“So it was a very pragmatic composing project,” Harbison said. “I actually sent a representative to the party to see how it went over.”

It has gone on to become a welcome holiday treat — a tasty reimagining of a beloved carol.

TOP: John Harbison works at his desk: His Little Fantasy on The Twelve Days of Christmas was written to settle a debt.