Your answer to this will of course depend in part on your own interpretation of the text, but I am happy to provide you with some ideas!
David Foster Wallace’s “The Devil is Busy Man” is about the rampant insincerity in American culture and how people in the United States often work hard to appear sincere about their intentions when they really have ulterior, selfish motives. This insincere, self-motivated way of living recalls the behavior of the devil, who is well-known in religious and secular legend to be a trickster figure.
For example, in the Bible’s creation story, the devil disguises himself as a serpent to trick Adam and Eve into disobeying God. In many well-known stories like this, the Devil is always hard at work being insincere and tricking people into doing things that help him or make him look good. This recalls what the narrator says in Wallace’s story:
As everyone is well aware, it is so difficult to do something nice for someone and not want them, desperately, to know that the identity of the individual who did it for them was you.
In equating the insincerity in the United States with the way the Devil behaves, David Foster Wallace condemns insincere, selfish behavior. In doing this, he also suggests that the problem with the United States is that people are always working to construct a fake appearance instead of working to be more genuine.