What themes are in Act III, Scene 1, of Romeo and Juliet?

Pride and honor are two themes of this scene. Tybalt wishes to fight Romeo in order to salvage his family's honor, which he believes to have been impugned by Romeo's appearance at the Capulets' party the night before. His pride compels him to confront Romeo over this slight. When Romeo refuses to be baited by Tybalt's insults, Mercutio steps in to fight in his place as a result of Mercutio's own pride. He considers Romeo's refusal to defend himself as a "Dishonorable, vile submission." After Mercutio's death, Romeo feels his own "reputation [has been] stained / With Tybalt's slander" and fights him out of pride as well.
Justice is another theme of this scene. After Tybalt kills Mercutio, Romeo tells Tybalt, "Either thou or I, or both, must go with him," because someone must accompany his soul to heaven. Romeo thinks it is unfair that Mercutio, who had nothing to do with their quarrel, should be forced to die alone; it is only just that one or both of them die, too.  When the prince arrives, Benvolio argues that Tybalt's death at Romeo's hands was just because death would have been his punishment anyway for having killed Mercutio. In the interest of justice, then, the prince condemns Romeo to be banished, not killed.