Music in opera is the foundation for interpretation in both the acting and singing. Composers have created an interpretation of the libretto through their music that should be manifested in the acting. Each note, chord, chord progression and key designation of the great opera composers has been selected to express an emotional situation in the life or mind of the character. The music gives the words a subtext of meanings that words by themselves cannot convey.
If the underlying music is ignored or slighted, there is a conflict between the music and any action taking place on stage. Expressive music becomes meaningless if the acting ignores its structure and energy.
The body is one of the three acting instruments (along with the voice and imagination) that singers must develop to become effective singing-actors. Every movement of any part of the body expresses an emotion to the audience. One of the primary goals of an opera singer is to train the body to freely and immediately express emotions through body movement.
Movement with no specific purpose is meaningless - "operatic gestures" of indiscriminate arm wagging, rocking back and forth, nervous tics and gestures. These types of movements are distracting.
An artist is someone who is in control of the techniques of singing and acting. Developing a solid, dependable acting technique will allow a singer to work with any type of director, in any type of opera, with any type of character and be an effective performer. It is important to know what works best and how to achieve the desired results.
Without a coherent acting technique, singers are not in control of their emotions, their bodies, or their imaginations, which means that their habits control their performances.