Act 3 Scene 4 is significant in the context of the whole play because it contains the turning point of Desdemona and Othello's relationship and also highlights Desdemona's tragic flaw of being too naive.
From the moment it is introduced into the plot, the handkerchief given to Desdemona by Othello becomes the play's most important symbol. Act 3, Scene 4 assumes the bizarre shape of a perverted trial. From the moment Othello enters, he plays the role of a prosecutor, demanding that Desdemona produce the handkerchief and accusing her of being a whore. Shakespeare's integration of the significance of the handkerchief only in this scene helps to contribute to the dramatic ironies in the play, as Othello did not tell Desdemona the meaning of the handkerchief when he gave it to her in the first place, but only in such a circumstance that he believes she has lost it. Instead of defending herself against her husband's accusations, Desdemona's response by advocating Cassio’s case. The result is a shouting match, wherein husband and wife completely fail to communicate, Othello repeatedly screaming “The handkerchief!” while Desdemona enumerates Cassio’s noble qualities, all of which Othello takes as testimony against her. Shakespeare's chosen diction "zounds" as Othello's final word before his exit highlights Iago's absolute influence upon Othello, as Iago is the only character in the play who uses this strong swearing word. In addition, the fact that he swears directly to his wife and then exits conveys the poor state of their relationship.
Throughout the play, Desdemona is presented by Shakespeare as a naive character who has a pure heart, Act 3 Scene 4 exemplifies this characteristic of hers as being a major tragic flaw. In this scene, she tells the clown to deliver a message to Cassio without hesitating if the content of message would be twisted. Then, when Othello accuses her of infidelity, she does not pick up the clues in his lines and indeed, goes on to plead for Cassio. Later on in the scene, when she talks to Iago - she eventually persists him to find out what "hath puddled his clear spirit" as she believes it is concerning state affairs, not aware of the fact that Iago could further inject poison in Othello's ears of her unfaithfulness. In Shakespeare's construction of Desdemona's statement towards Iago, "men's nature wrangle with inferior things", he has emphasized the dramatic irony as we, the audience, know that Othello is wrestling an inferior thing, his own emotions; yet, Desdemona only believes Othello's "great ones" are to do with the states and does not realise that his emotion for her is an "inferior thing".
By the end of this scene, the plot unfolds without any further assistance from Iago, although he is still involved in manipulating it in some way. He has thus far been so careful to inform the audience of his every plan that it seems like he must have anticipated every turn in the road. As with the characters onstage, Iago’s power with the audience lies in his ability to make them believe he knows more than he does.
