The reader should especially note that Prospero seeks penitence, not revenge:
The rarer action is
In virtue than in vengeance. They being penitent, The sole drift of my purpose doth extend
Not a frown further. (V, 1: 27-30)
Prospero seeks justice, but that justice is more than balanced by the mercy that Prospero shows toward Antonio and Alonso. Justice is subservient to mercy. Shakespeare also placed a similar emphasis on the concept of mercy in his other plays, most notably in the following:
The quality of mercy is not strained.
It droppeth as the gentle rain from heaven Upon the place beneath.
(The Merchant of Venice: IV, 1: 179-81)
Mercy is, then, a heavenly attribute; and Prospero bestows mercy upon those who are penitent. Even Caliban receives mercy at the end of the play although one cannot help but wonder if his penitence is genuine: “I’ll be wise hereafter and seek for grace” (V, 1: 298-99). Prospero, however, extends his mercy to all as his final act of leadership on the magical island.
Shakespeare often employed a Two Worlds Theme in his comedies, such as in A Midsummer Night’s Dream. In that comedy the strict Athenian law and rigid social order under the leadership of Theseus, Duke of Athens, is transformed into a gentler and kinder society after the principle characters journey into the magical forest that is inhabited by fairies. Shakespeare thus employs a three-part structure for the play:
The Two Worlds Theme also implies a theme regarding social transformation. The happy ending for the characters involved also implies a better and improved social order for all of the inhabitants.
The Two Worlds Theme is implied in The Tempest: (1) Milan and Naples, (2) the magical island, and (3) the return to Milan and Naples. And the play ends with the suggestion that the corruption in the two Italian cities will come to an end.