Authors can use different literary devices to either establish an underlying mood throughout the whole work or to create certain shifts in mood. Elements such as diction, imagery, rhetorical schemes, and figures of speech can all be used to create mood. Therefore, when analyzing for mood, it's important to zero in on these devices. We can use these devices to conclude that some of the emotions that characterize the mood of Act 3, Scene 3 are devastation, frustration, and anger.
One thing that helps characterize the mood of this scene is Romeo's reaction to his banishment. Friar Laurence wants him to view it as it is, a blessing, while Romeo is bent on viewing it as torture. Romeo's mood and perspective is especially portrayed in Shakespeare's use of imagery and the parallelism in Romeo's lines:
There is no world without Verona walls;
But purgatory, torture, hell itself.
Hence banished is banish'd from the world,
and world's exile is death. (III.iii.18-20)
Romeo's choice to relate being banished to the images of "torture" and "hell" certainly help portray his devastated mood. But these lines are especially effective because of the parallelism in Romeo's argument. Romeo's first clause of the first line speaks of being banished in the phrase "without Verona walls," which he relates to hell in the second clause. In the first clause of the second sentence, he again speaks of banishment in the phrase "banish'd from the world" while ending with a second clause about death. Since one can't reach hell without dying, Romeo has created a perfectly even, perfectly parallel argument.
However, the scene's mood is characterized by more than just Romeo's feelings of hopelessness. It is also characterized by the anger and frustration Friar Laurence feels towards Romeo. His anger and frustration can especially be seen in the diction Shakespeare chose for the line, "O deadly sin! O rude unthankfulness!" (25). Friar Laurence is calling Romeo's reaction a deadly sin because it is vain and arrogant to call God's gifts of mercy torture. Hence, Shakespeare's word choices for Friar Laurence's description of Romeo help us to see the friar's mood of anger. We further see the friar's reaction in his line, "This is dear mercy, and thou seest it not," showing us that the friar certainly considers Romeo's sentence to be a gift worth being happy for (25).