Claudio announces that he noticed Hero before the war, but he was busy with war stuff. Now he can get busy with love stuff. Overall, he falls in love with Hero quickly. Beatrice and Benedick, by contrast, seem to have spent a long time developing their enmity towards each other. Beatrice alludes to some past interactions she may have had with Benedick that have soured her both on him and on love. Essentially, they hate each other fiercely, and this is only Act I.
Claudio hasn’t even properly announced his love for Hero and he’s already sure it's over. When everyone’s at the masquerade ball, and Don Pedro is wooing Hero in Claudio’s name, Don John slips over and plants the suggestion that Don Pedro is getting Hero for himself. Claudio becomes suspicious and immediately writes off his love for Hero and his friendship with Don Pedro. Worse, we realize he’s kind of a wuss for not even being willing to fight for the girl he loves.
Some more conflict develops in the parallel plot of Beatrice and Benedick, in a kind of inside-out way. In a traditional plot, conflict happens when two people who love each other end up hating each other. In this case, once Hero and Claudio get their marriage stuff straightened out, all attention turns to getting Beatrice and Benedick to fall in love. They kind of start to – and what’s creating conflict is that this whole time they’ve hated each other, and now suddenly have to deal with the fact that they might be in love.
The inexplicably villainous Don John won’t give up just because he’s failed to ruin Hero and Claudio’s relationship once. Instead, he’s worked out a plan to frame Hero as disloyal, and he puts it into action by having Claudio and Don Pedro witness his little set up.
In the meantime, our two favorite characters, Beatrice and Benedick, are falling in love. The problem is, they haven’t admitted it to each other yet, and instead it’s just ruining their personalities. Through the middle section of the play, both Beatrice and Benedick become dull and lose the spark we’ve come to appreciate about them, because they’re stuck in that unrequited-love phase. We may be kind of rooting for them to get together eventually, but their love is complicated by the possibility that it might make them boring and typical, thus robbing them of all the qualities that made them fall in love with each other in the first place.
First of all, this scene is climactic because it’s so out of character for Claudio. We’ve known Claudio up to this point to be kind of wimpy – he doesn’t stand up for himself when Benedick teases him for being whipped, he doesn’t have the cajones to tell Hero himself that he loves her, and he doesn’t even fight for Hero when he thinks he's lost her to Don Pedro. Our notion of Claudio is blown open in the wedding scene, because he has fierce feelings – and acts on them. In fact, this is the first time he’s even engaged in a real conversation with Hero (when they decided they would get married, Hero didn’t say a single word). Claudio’s explosion, provoking the taciturn Hero to react, is kind of a big deal.
This scene is also climactic because of what actually happens. Claudio loses a wife, Leonato loses his daughter and his reputation, and Hero loses her "life" – or at least her ability to have a normal life from now on. High drama, all over the place.
As far as Beatrice and Benedick go, this same scene is a climax in their relationship too. All of this turmoil has put pressure on Benedick to reveal his love, especially because of how upset Beatrice is. The only thing that can comfort her has to be as powerful as the thing that’s upset her – and the straight declaration of love from Benedick is strong enough to startle. Beatrice responds equally climactically – she’s full of fury, and demands that Benedick kill Claudio if he loves her. She won’t hear reason, so Benedick agrees to challenge his friend to a duel.
All of the characters are so emotional right now that you’re on the edge of your seat, or your page. The plot has gotten so thick that unraveling is going to be a challenge. Whatever the solution is, it’s going to have to resolve a lot of issues: Hero will have to come back to life publicly; Claudio and Don Pedro have to be redeemed as decent people; Don John and his henchmen have to be brought to justice; and the rift between Benedick and Claudio has to be sealed. Also, Beatrice and Benedick’s new-found love is going to have to survive the strain of the "murder" of Hero and the impending attempted murder of Claudio.
Everything is nearly fixed when Borachio admits the whole plot, full of apology, to Don Pedro and Claudio. Faced directly with their misjudgment, Claudio and Don Pedro feel really, really bad, and have to try to make it up to Leonato. Leonato relaxes the whole situation by giving Don Pedro and Claudio an out – mourning Hero publicly to clear her name publicly, and Claudio will get a second chance at being in Leonato’s family by marrying his mystery niece.
Further, we know there’s no real harm done in the relationship between Hero and Claudio; Claudio will be excused for having simply made an error in judgment, so Hero won’t hate him forever. Everyone’s just happy the girl can get married again, so it’s like all systems are back to the status quo. Also, Benedick no longer has to kill Claudio, which significantly relaxes everyone.
With everything cleared up, Hero reveals she is still living and still as innocent as on her original wedding day. Benedick and Beatrice approach their conclusion on a more tense note; Benedick proved his love for Beatrice by choosing her (and justice) over his friends, but their relationship is put to the test by Benedick’s public declaration of love. To admit that they no longer hate each other, and that they actually might be in love, is a huge concession for Beatrice and Benedick. Though they started the play hating each other, and they’ve come around to happily loving each other, this scene of publicly getting together makes us certain that these two characters won’t be tamed by domesticity, but will actually preserve all of the acidity we love about them. Finally, it’s tacked on to the end of the play that Don John has been caught and is awaiting his punishment, which reminds us that there is justice in the world.