Shakespeare re-examined certain themes over and over, in both his tragedies and comedies. One of the predominant themes is appearance versus reality, and another common theme is jealousy. All of Shakespeare's comedies revolve around love relationships, since, by definition, a comedy must end in at least one marriage, but a twist on the traditional love relationship that Shakespeare often employs as a theme is the battle of the sexes (mostly as a witty war of words) as a sign of true love.
Appearance versus reality is announced as a theme of this play in the very title: Much Ado about Nothing (or Noting, which is how the word would have been pronounced). Many characters are taken in by scenes enacted by other characters in order to fool them into believing something that is potentially false. In Act II, scene iii, Benedick is duped by Leonato, Don Pedro and Claudio into believing that Beatrice is desperately in love with him. Act III, scene i has Ursula, Hero and Margaret pulling the wool over Beatrice's eyes about Benedick, and the end of Act III, scene ii suggests that Don John will show Don Pedro and Claudio a scene in which Hero will enact her unfaithfulness. This scene is not enacted onstage, but all of these scenes highlight the theme of appearance versus reality.
Jealousy is thematically examined in the responses of Claudio to what he suspects is Hero's involvement with other men in both the dance sequence of Act II, scene i and the scene mentioned above, but also in the actions of the comic villain, Don John, who is jealous of the place that Claudio holds in her brother Don Pedro's affections.
The battle of the sexes in this play is enacted (famously) between Beatrice and Benedick who, even as they are pledging their troth to each other in Act V scene iv, are still finding ways to battle each other, and must have a truce signaled by Benedick's line, "Peace! I will stop your mouth," after which he kisses Beatrice.
For more on these and other themes, please follow the links below.