Early in the story the tone is "normal" and reflects the work setting. The scene is set in a typical office with typical workers, albeit each with idiosyncrasies. In short, it is a normal office setting. The tone shifts from normal to bizarre and even increasingly absurd as Bartleby begins to "prefer not to" do things. A subsequent question for the reader is whether Bartleby's behavior is absurd or if it is a justified, although odd, response to his absurd circumstance.
One of the themes of this story is the alienated man/woman in modern society, that is to say, the feeling of being an insignificant cog in an indifferent industry and society. Bartleby's role as scrivener is fitting because he is essentially a copying machine, stripped of any human affectations in his work. He simply copies things. He needs the job to survive but does attempt to rebel against this machine-like role by refusing certain tasks. It is ironic (or fitting if we consider Bartleby sarcastic) that he refuses his machine-like work in a repetitive, copying, machine-like manner.
When the lawyer discovers that Bartleby has been living in the office, he compares the image to ruined remains - "a sort of innocent and transformed Marius brooding among the ruins of Carthage!" This is symbolic of Bartleby's lifestyle, but this (ruins) as a symbol of the inhuman modern industry itself is lost on the lawyer. The lawyer is continually dumbfounded as to why Bartleby is refusing to participate in this alienating work.
Supporting the theme of Bartleby as a doomed cog in the industrial machine is the fact disclosed by the lawyer at the end of the story - that Bartleby had been a clerk in the "Dead Letter Office" and the fact that Bartleby ended up in the "Tombs." There is consistent imagery of death, mindless (lifeless) repetition, and Bartelby's pale complexion and personality; all support the theme of the lack of humanity in industrial affairs.