Many of the scenes in Othello work by the pairing of two characters who are basically different in values or hidden agendas, putting them together through an experience or event, which has a different significance for each. Such pairs are Iago and Roderigo, Desdemona and Emilia, Othello and Iago, and Iago and Emilia.
Iago is paired with Roderigo for purposes of exploitation. By talking to him, Iago can show the audience his wicked intentions, yet Roderigo is so gullible that he is an easy dupe. Desdemona and Emilia are newly in each other's company, but quickly develop a friendly style of conversation that contrasts their different approaches to life. Emilia is down to earth to Desdemona's nobility, and practical to Desdemona's romanticism. Yet, when a crisis comes, they both share the same basic values of honesty and loyalty.
Iago and Emilia, although married and appearing to be similar personalities on the surface, see the world differently. Iago has the reputation of the "rough diamond," who speaks directly and honestly, but he uses his reputation as a disguise for his plotting, whereas the "rough diamond" really is Emilia's true nature. Their conversations are oppositions of opinion about the nature of men or women, or attempts by Iago to control Emilia's actions, balanced — until she discovers his true nature — by Emilia's willingness to do things to please her husband.
The development of the Othello-Desdemona pair is more hidden, and more complex. There is a polite formality of words between these two which persists below the endearments of the first half and the abuse and anguish of the second. At a certain level, they always treat each other as respected strangers, and as circumstances drive them apart, only this formal politeness remains as a frame for communication in the final act, where they go in different emotional directions, despite their underlying love for each other.