Speech and Dialogue
This is a play, and plays usually have a whole lot of dialogue. Mamet even goes a little farther though, and utilizes language as a means to just about everything. These guys talk to sell, they talk to fight, they talk to buy time. They just talk and talk.
We learn a lot about people from what they say and what others say about them:
LEVENE: You have no idea of your job. A man's his job and you're fucked at yours. (2.1.519-520)
From that one line, we learn that Levene believes that a man is defined by his work. We also learn that he believes Williamson is a failure at his job, so we can infer that Levene believes Williamson is a failure as a man. This is a sentiment shared by Roma, as well.
If your mom's anything like Shmoop's mom, she probably told you from time to time that actions speak louder than words. And, as is so often the case, she was right—we really can learn a lot more about a person from what he does than from what he says sometimes.
Let's take Roma as our example. He says a whole lot, right? He brags, he knocks on people, he doles out advice. However, nothing quite defines him like his seemingly instantaneous choice to get Levene to pretend to be a client in order to trick Lingk.
Roma sees Lingk and doesn't even hesitate. This shows us that Roma is quick on his feet, always thinking about work, and ready to completely lie and take advantage of another person in order to get what he wants. Levene's readiness to jump into the lie shows us that he's not much different from Roma. It also hints at the fact that these guys have probably done this before.