Who steals my purse steals trash
Good name in man and woman, dear my lord,
Is the immediate jewel of their souls.
Who steals my purse steals trash; 'tis something, nothing;
'Twas mine, 'tis his, and has been slave to thousands;
But he that filches from me my good name
Robs me of that which not enriches him,
And makes me poor indeed.
At this point in Othello, our hero has just begun his precipitous fall into Iago's intricate trap. Iago hints that one of Othello's officers, Cassio, has been making time with Othello's wife. On top of this innuendo he plasters a seeming reluctance to reveal the fictitious affair, because that would ruin Cassio's reputation—and to "filch" from someone his good name is a much more serious crime than stealing his purse. Honor is an essential possession, something that can belong to you and to you only; your money, on the other hand, remains what it is even if thousands of others have handled and possessed it. Compared to honor, then, money is mere "trash."
Iago's speech is in ironic contrast to his exhortations of Roderigo to "put money in thy purse [see PUT MONEY IN THY PURSE]. When it suits his purposes better, Iago can exclaim that virtue's "a fig" (Act 1, scene 3, 319), and that reputation is merely something one cultivates in order to hide his true intentions. It rather suits his purposes here, however, to cloak his evil intentions—his desire to ruin Othello's marriage—in the pieties of friendship and sacred respect for another man's honor.