I believe that the handkerchief plays one of the major roles in the play. Othello was skeptical about if Desdemona was cheating on him or not. Iago was just putting worried thoughts into Othello's mind about Desdemona and Cassio, but when Othello realized that Cassio had it he, thought that it was for sure that she was cheating on him. Iago used it to give to Cassio, and make it look like Desdemona gave it to Cassio. Othello was hiding while Cassio and Iago were talking, and when Cassio gave the handkerchief to Bianca, Othello thought that Cassio was just using Desdemona, and that he had no feelings for her. This enraged Othello to the point that he wanted revenge. Othello is now planning to kill Desdemona and Cassio, all because of that one handkerchief.