One of my favourite speeches in this play which can easily be connected to the themes presented is the speech of Prospero in Act IV scene 1 when he declares the end of the wedding masque. Let us remind ourselves what he says at this crucial point in the play:
Our revels now are ended. These our actors,
As I foretold you, were all spirits, and
Are melted into air, into thin air;
And, like the baseless fabric of this vision,
The cloud-capped towers, the gorgeous palaces,
The solemn temples, the great globe itself,
Yea, all which it inherit, shall dissolve;
And, like this insubstantial pageant faded,
Leave not a rack behind. We are such stuff
As dreams are made on, and our little life
Is rounded with a sleep.
Prospero utters this speech as he remembers the plot against his life that he has to deal with, and perhaps we can relate the sadness in the tone of this speech to the way in which Prospero seems so enraptured in the fruits of his magic that he is distracted from the real and messy situations of life that he has to deal with. This speech is significant because it marks a turning point in the play as regards Prospero's character. From this point on he repeatedly refers to a future time when his "labours" will be ended and he will relinquish his magic powers. Prospero is shown to want to dispose of his power and to be able to return to a normal existence in his home of Milan. This speech therefore points towards both the incredible beauty of the world he has created through his magic arts, but also indicates a sense of sadness, as he realises that actually this beauty is insubstantial.
The thematic significance of such thoughts becomes very obvious when we take into account the numerous references to drama and acting such as the "great globe." Prospero's island and the theatre are clearly related to each other, and the same kind of magic that Prospero uses to entertain Ferdinand and Miranda is the same kind of magic used by Shakespeare to entertain his audience. When Prospero choses to relinquish his power, the magic will end, and his characters are returned to reality, just as at the end of the play, the audience is forced to return to their normal lives, no matter how convincing the illusion has been.