Pg. 173, vol. 2:
Speaking of Opera Seria.
"The highest arbiter of taste and practice was the ruler or patron; next in order of clout came the audience; next the singer; next the librettist. The composer was there to serve them all."
It's interesting to me that we know think of the arbiters of taste in almost the opposite order. Such ideas are the effects post-enlightenment education. Perhaps the most pertinent idea here then, is that much of the music we consider Art, and many of the techniques used in most of music we listen to, comes from a time when the composer was very far down the ladder of power.
The reception of Opera itself in the early 1700s is testament the place music occupied in society. The only times audience members were really required to pay attention was when the king or patron, who the opera also presented as a symbol of all that is good in the world, was in attendance. Otherwise, people were free to talk, wander in and out, play cards, and relieve themselves in chamber pots. Most audience members also new all of the operas extremely well, meaning they could pop in or out whenever they pleased depending on when their favorite arias or singers were on.
Singers themselves thus needed to draw the audience in with virtuosity, improvisation and diva-like behavior. Caffarelli, a virtuoso castrati of the day, was arrested for refusing to sing, mocking other performers, and practically molesting a female singer on stage, only later to be reinstated by the opera company because he was the public's darling.
So, singers behaved, musically and personally, much more like pop singers do today, and the reception of music was more akin to the way we watch television than the way we sit in an opera house.