What is the importance of a play within a play in A Midsummer Night's Dream?
The first “importance” is the entertainment value for the Elizabethan audience, who hugely enjoyed comic antics, especially when they made fun of the London tradesmen, who were socially a cut below the noble aristocracy and the merchant class. Secondly, the play retells a famous plot – Pyramus and Thisbe – thereby bringing up a popular classical reference. But most importantly, it points up two features of the main plot: role-playing in society, and the inefficiency of ocular proof as a means of understanding how the world works (note how many misunderstandings caused by false "seeing" there are in all three plots). These rustics have come into the woods (meaning out of society’s eyes, but also out of their natural environment) to prepare an entertainment for the coming wedding of Theseus and Hippolyta, as far above them in class as they could be (thus reinforcing the seriousness of the public ceremony, by mocking “love” in the lower classes). Then, when the fairy plot is added, the audience sees love and marriage in all its aspects: holy, but also comical, and also a “mirage” indulged in by the participants. This triple dramatization is more than clever on Shakespeare's part. It demonstrates his sensitivity to the way of the world, to the universals that transcend class. It is a portrait and a cartoon at the same time.