During the military discussion, the audience discovers that Cyprus is of supreme value to the Venetians, and it is vital that it remain under Venetian control for protection of sea trade. Therefore, when command is conferred on Othello, the Duke is making a public statement that Venice relies on him completely. Othello rightly feels confident; whatever his marriage arrangements, he knows that the Senators will back him because they need him.
After they deal with the military crisis, the Senators consider how to avenge an injustice done to one of their members: Brabantio. By the time he arrives at the emergency meeting, Brabantio's rage has turned to grief, and the Senators treat Brabantio's grief as a personal loss, rather than a public matter. They think his daughter must have died, and, for Brabantio, it is as if she had died. He believes that she has so gone against nature that witchcraft must be to blame. The Duke, speaking with sympathetic indignation, promises Brabantio that he shall judge the offender, even if it were the Duke's own son: "the bloody book of law / You shall yourself read in the bitter letter / After your own sense" (68–69). This declaration is significant because witchcraft was a capital crime; the law on this topic was indeed "bloody" dealing with how a witch was to be tortured and eventually executed. Yet the Duke's rash promise to Brabantio immediately rebounds when Brabantio points to Othello: "Here is the man: this Moor" (71). Suddenly the commander appointed to save Venice from her enemies is under risk of execution. The Senate risks losing a war to satisfy one man's desire for revenge, so the Duke hopes that Othello can justify his actions.
Othello's defense speech is in two parts: the first (76–93) establishes him as a soldier successful in the service of Venice and respectful of the great men of the city, and the second (127–169) describes how stories of his adventures won Desdemona's interest and then her love.
