What is Gregor's interpretation of why the attorney comes to check on him personally, rather than some lesser messenger? How is the choice of limited-omniscient narrator important here?

Are you referring to the chief clerk in chapter one? When the chief clerk arrives only a short time after the company has opened, Gregor is angered that suspicion is cast on him for wasting only an hour of the firm's time. Time, of course, symbolizes the capitalist order in which time is money and is thus valuable. Oversleeping is a crime because by oversleeping one misses business and thus wastes money. Gregor sees the clerk's visit as a slight on his character rather than a concern for the company. The limited-omniscient narrator lets us see the absurdities of the world through a character, Gregor, who is quickly becoming completely alienated from it.