Possible Clues:

• Certain Beethoven work
• Scarlatti's 'Capriccio,' e.g.
• Uplifting numbers at a musical performance
• Beethoven's "Moonlight," e.g.
• Haydn piece
• Therefore Nathaniel took a piece of music
• Boy attending a musical performance
• Work for soloist
• A thank-you to the boy for the composition
• Music for a soloist