This scene represents the turning point for Othello as he borders on doubt and uncertainty about Desdemonas unfaithfulness. Othellos indecision and lack of judgement is communicated through repetition: I think that my wife be honest and think she is not; I think that thou art just, and think thou art not. His inherent insecurity is reflected in this scene, showing the vulnerable nature that Iago takes advantage of.
Iagos character plays on many of Othellos emotions to successfully manipulate him and drive him to insanity. Iago pretends to be insulted by Othellos distrust in him, crying about the awful world in which one is punished for well-intentioned honesty. In the lines, I thank you for this profit, and from hence Ill love no friend, sith love breeds such offence, the use of rhyming couplets, usually to mark the end of a scene in Shakespeare, gives the impression that he is about to leave, evoking curiosity in Othello to want to hear more about what Iago has to say.
Manipulation as a theme is strong in this scene as Iago uses Othellos confusion and growing doubt in Desdemona to his benefit. The use of pathos in the quote, O wretched fool, that lovst to make honesty a vice! shows how Iago is victimising himself in order to play on Othellos emotions and his once strong trust in him. Iagos speech appeals to reason to cause Othello to think logically rather than allowing his feelings for Desdemona affect his judgement. This is also an example of dramatic irony as we already know of Iagos plan to manipulate Othello, Desdemona and Cassio.
This relates to the overall theme of jealousy in the play. It is essentially what destroys Othello, fuelling his insecurity, overreaction and violent instincts. Therefore, his common sense and respect for justice is blinded, leading to insanity. Othellos reaction to the state of uncertainty is to think of ways of suicide, indicating his irrational and thoughtless thinking. Iagos language following on is vulgar, provoking him and causing his temper to rise.