Greenberg makes clear that Italian comedia del arte was a medieval predecessor of opera and the first real operas were grand affairs that were sponsored by and enjoyed by the aristocracy. During the period of the European Enlightenment, around 1750, ideas and situations began to allow merchants and other increasingly wealthy and powerful non-aristocrats to have more of what appealed to them. Mozart's The Marriage of Figaro is a prime example of arresting music that is still completely excellent by today's standards coupled with plot and lyrics that appeal to more widespread classes of people. Basics of the opera are explained in the movie "Amadeus" as well as many other sources. The opening scene of the lovers and servants in the household is a famous one. It shows Figaro happily planning the installation of their marriage bed in a room ideally located between the bedrooms of the mistress of the house and the master. His soon-to-be wife informs him that the room is a trap to be used by the count when Figaro is conveniently absent to force his attentions on her. Figaro lets us know very clearly that he is outraged and more and will deal with the situation.
I have listened to the opera often and only in Italian, a lovely language that I don't understand. Still, the tunes and expressions haunt me. Give it a try sometime. You can hear a short sample on the link above and there are many other ways to hear this classic that has lasted several centuries and is loved in many countries of the world.