When a composer has a great dance tune with no place to go, it's time to write a serenade. Serenades are on the populist end of classical music, which is why the San Francisco Symphony is devoting one of their summer pops concerts to them. Eine, kleine Nachtmusik is a case in point: We don't know why Mozart composed it, but since tunes dropped from his brain like water droplets off a wet collie, he didn't really need a reason, did he?
The same thing goes for Dvorak's Serenade in E Major and the Tchaikovsky Serenade for Strings, two of my favorite pieces from the 19th Century by two of the century's better tunesmiths. (If the S.F. Symphony had put Vaughan Williams' Fantasia on a Theme of Thomas Tallis on the program, they'd have hit the string serenade equivalent of a home run, but “enough is as good as a feast,” they say.)