Read it through once

IAGO: You are a man; you are of my mind; you are my friend; and I'll tell you what you suffer for: You are jealous of my success with Othello; but that is not the cause. I follow him to serve my turn upon him: we cannot all be masters, nor all masters cannot be truly followed. You shall mark many a duteous and knee-crooking knave, that, doting on his own obsequious bondage, wears out his time, much like his master's ass, for subjecthood. I am one, sir, that comes to tell you this: I do follow the Moor to serve my turn upon him.