This last scene is a lengthy one that might have been substantially shorter had the duke gone directly to the matter, simply explaining his disguise, the crimes he has witnessed, and going about the administration of justice. The scene, however, would have been less effective. As it is, Shakespeare builds suspense by leaving the characters of the play and its audience in doubt as to the outcome. He emphasizes his presentation of Christian mercy by having Isabella plead for Angelo while still under the impression that he has executed her brother. And he creates a mildly comic scene to finish a play that might have ended in tragedy and that would certainly have had a rather flat finale if the duke had simply narrated his part and doled out his punishments.
A comic undertone is provided by the audience's knowledge of the duke's identity. In his disguise, he alludes to it ironically: "The duke / Dare no more stretch this finger of mine than he / Dare rack his own" (315-17). Later, he protests to loving the duke as he loves himself. Lucio's accusations against the friar-duke made to the duke himself provide further comedy for the audience, which knows what the actor does not. When Claudio is revealed to be still alive, the duke's speech to Isabella has a gentle and sympathetic humor that any audience would surely warm to: "If he be like your brother, for his sake / Is he pardon'd" (495-96).
In this final scene, the theme of merciful justice comes to the fore. The duke seems ready to deal harshly with Isabella, Mariana, Friar Peter, and Friar Lodowick, and to apply the letter of the law in the cases of Lucio and Angelo. The mercy that he finally shows to all contrasts sharply with the rough hand of the law that he at first threatens.
