The title of the play, given that "nothing" was pronounced as "noting" in Shakespeare’s day, clues us in to the fact that noting is central to all of the action. Noting is a motif throughout the entire play in the form of observation (when Claudio asks if Benedick noted Hero, when Friar Francis says he’s been busy noting Hero at the wedding, etc.), through music (as Benedick jokes about sheep’s guts as strings on an instrument, when Balthasar plays his notes, etc.), and also through written notes (like the letters that ultimately reveal Benedick and Beatrice’s love at the end of the play).
Ultimately, the play revolves around misnoting – the problem of people wrongly interpreting what another person does or says. Benedick and Beatrice are manipulated into noting false conversations about their mutual love, and Don John sets up Claudio and Don Pedro to wrongly observe (or misnote) Hero’s loyalty. The play constantly points out the difficulty of observing correctly, as observation is always subject to interpretation, and interpretation is often wrong. This doesn’t mean that misnoting can’t have good outcomes – after all, Beatrice and Benedick do get together as a result of it – but Shakespeare is essentially laughing at the follies that result from misnoting.