What is the moral lesson of the story the miracle worker?

The real moral lesson of "The Miracle Worker" is the age old one of perseverance. Anne Sullivan not only overcame her own disability, but enabled an imprisoned child to learn, grow, and become a fabled author and public speaker. When one perseveres, one can attain heights others only dream of. No one starts out wanting to be famous, but by application and diligence miraculous things happen. To learn to do a thing and do it well will be it's own reward, and the eagerness to impart a skill to others will inevitably get one remembered.