He was a tool of the boss, without brains or backbone. (1.6)
The inhuman aspect of Gregor's job is emphasized here. You could say it's worse than being a vermin: Gregor is reduced to a mere, inanimate "tool."
Why was only Gregor condemned to work for a firm where at the slightest omission they immediately suspected the worst? Were all employees louts without exception […]? (1.15)
Another dehumanizing aspect of work for Gregor is that it reduces individuals to "louts." Of course, the irony here is that the office manager notes that Gregor is suspected of stealing cash payments from the company.
The boss would […] cut off all excuses by quoting the health-insurance doctor, for whom the world consisted of people who were completely healthy but afraid to work. (1.6)
Gregor feels that he's part of a society that is geared toward work, work, and more work. It's not only his boss who sees him as a mere "tool" (see Quote #3 above). The medical profession is also implicated in that its sole purpose is to prepare human beings for work, rather than cure them.
Over the table, on which an unpacked line of fabric samples was all spread out – Samsa was a traveling salesman (1.2)
We don't get many details about Gregor's room, but the few details that we do get suggest that Gregor has very few extracurricular activities. He's a man devoted to his work and not much else.
"Oh God," he thought, "what a grueling job I've picked! […] I've got the torture of traveling, worrying about changing trains, eating miserable food at all hours, constantly seeing new faces, no relationships that last or get more intimate." (1.4)
The life of a traveling salesman should look awfully good to someone who just got turned into a vermin, but that's not the case for Gregor. Gregor views the transient life of a traveling salesman as, well, dehumanizing. It's an asocial and physically grueling lifestyle.
"A man might find for a moment that he was unable to work, but that's exactly the right time to remember his past accomplishments and to consider that later on, when the obstacle has been removed, he's bound to work all the harder and more efficiently […] the traveling salesman, who is out of the office practically the whole year round, can so easily become the victim of gossip, contingencies, and unfounded accusations, against which he's completely unable to defend himself." (1.27)
In his eagerness to defend himself to the office manager, who's waiting outside his bedroom door unaware of what's happened, Gregor rattles off a great little speech about hard work. The speech is quite ironic because 1) it's hard to imagine what lessons can be learned from overcoming vermin-hood, and 2) the rumors about Gregor's delinquency really can't compare to the fantastic reality of what's happened to him.
But Gregor understood easily that it was not only consideration for him which prevented their moving…what mainly prevented the family from moving was their complete hopelessness and the thought that they had been struck by a misfortune as none of their relatives and acquaintances had ever been hit. What the world demands of poor people they did to the utmost of their ability […] but for anything more than this they did not have the strength. (3.6)
Just as Mr. Samsa has trouble getting out of bank messenger mode when he's at home (see Quote #7), the Samsas as a family have a hard time letting go of their class status. Accustomed to a middle class lifestyle, they are unable to adjust themselves to their new financial conditions.
These serious gentlemen – all three had long beards, as Gregor was able to register once through a crack in the door – were obsessed with neatness, not only in their room, but since they had, after all, moved in here, throughout the entire household and especially in the kitchen. (3.9)
As part of their new poverty, the Samsas have to take in boarders – three "serious gentlemen." We don't learn anything about them except that they act really important and have long beards – sort of like ZZ Top without the sunglasses. Their sole purpose in the story seems to be to emphasize that the Samsas are no longer masters of their own home and are now subservient to the boarders. Like Gregor, the boarders are an alien presence whose needs take precedence over the other Samsas. Both the boarders and Gregor have to leave before the Samsas' social status can be restored.
[H]is father dozed, completely dressed, in his chair, as if he were always ready for duty and were waiting even here for the voice of his superior. (3.4)
With Gregor out of the picture, Mr. Samsa takes over as the breadwinner. Arguably, he is just as much a "tool" of his profession as Gregor was when he was a traveling salesman (see Quote #3). Even when Mr. Samsa is not at work, not even conscious, he is still his job – he's a bank messenger and nothing more.
This old widow, who thanks to her strong bony frame had probably survived the worst in a long life, was not really repelled by Gregor. (3.8)
Ironically, it's the old widow (i.e., the cleaning woman) who can stand Gregor, not the members of his family. How can a complete stranger be able to handle Gregor better than his own family? This passage suggests that she's experienced "the worst," and as Quote #8 above makes clear, the Samsas are unaccustomed to "the worst," to a catastrophe of Gregor's magnitude.