I cannot switch my voice. My voice is not like an elevator going up and down.

The renunciation also helped her finances as Maria Callas no longer had to pay US taxes on her income. Previously Maria Callas was shown in the commercial. "
Callas herself stated that in Opera Acting must be based on the Music quoting Maestro Tullio Serafin's advice to her:

"When one wants to find a gesture when you want to find how to act onstage all you have to do is listen to the music.

However her artistic achievements were such that Leonard Bernstein called her "The Bible of opera"; and her influence was so enduring that in 2006 Opera News wrote of her: "Nearly thirty years after her death Maria Callas's still the definition of the diva as artist—and still one of classical music's best-selling vocalists. The press exulted in publicizing Callas's allegedly temperamental behaviour her supposed rivalry with Renata Tebaldi and her love affair with Aristotle Onassis. Her dramatic life and personal tragedy have often overshadowed Callas the artist in the popular press.