The beginning of the play is Prospero wanting revenge and wanting to teach a lesson to his enemies with his storm, however, revenge melts away like the storm. Prospero does have justification for his revenge, being wronged by his friends and family. However, he chooses forgiveness, if they repent for it (arguing if true reconcillation is achieved). When Alonso, Antonio and Sebastian feel guilty, this is when Prospero decides to forgive them. For most of the play, it's not clear what Prospero wants to do, but he finally decides to forgive, deciding this is morally better than revenge. Shakespeare conveys that happiness is gained, not by revenge, but by forgiveness.