This scene is absolutely crucial to the overall plot and the rising action of the play. Note how when Don Pedro says he will leave after the marriage, Claudio is quick to offer to accompany him, which severely questions the "love" he has for Hero. It suggests that Hero for him is a prize to be won rather than representing a relationship to grow into and learn about. Of course, one of the biggest changes in this scene is the change in Benedick, who has now changed his appearance and no longer seems willing to play his role of jester for Don Pedro, saying only in response to the taunts that "I have the toothache." This is certainly a massive change as he has obviously tired of engaging in the witty repartee that he was so successful in. Love for Beatrice has wrought a fantastic transformation in his character, indirectly commenting on the "love" of Claudio for Hero.
Of course, the major element of this scene is the revelation of Don John's stratagem to overthrow the happiness of the assembled masses. It is important to note how cunning he shows himself to be. By appealing to the jealousy of Claudio and the good name of Don Pedro, he shows he knows their characters and the weaknesses well and has thought about what he needs to do to ensnare them in his plot. Don John dominates the dialogue, mastering the conversation and psychologically Claudio and Don Pedro too. Of course, the willingness of Don Pedro and Claudio to believe this claim says a lot again about the nature of Claudio's love for Hero but also the role of women in this society.