After playing on Cassio's vices, Iago tells him he would be better off advancing himself and his reputation through Desdemona, Othello's recent bride. Iago tells him that
I'll tell you what you shall do. Our general's wife is
now the general. I may say so in this respect, for that he
hath devoted and given up himself to the contemplation,(305)
mark, and denotement of her parts and graces. Confess
yourself freely to her; importune her help to put you in
your place again. She is of so free, so kind, so apt, so
blessed a disposition, she holds it a vice in her goodness
not to do more than she is requested. This broken joint(310)
between you and her husband entreat her to splinter
and, my fortunes against any lay worth naming, this crack
of your love shall grow stronger than it was before.
Iago is only arranging his chess pieces, however, because the reader is privileged to know that it was Iago's plan in the first place to slander Cassio. By having Cassio constantly seek Desdemona's ear, Iago can ply Othello's while he does so.