You're under arrest all right, but not the way a thief would be. If you're arrested like a thief, that's bad, but this arrest ---. It seems like something scholarly, I'm sorry if that sounds stupid, but it seems like something scholarly that I don't understand, but that I don't need to understand either. (2.4)
This is Frau Gruber's humble attempt to understand – or really, not to understand – K.'s trial. Frau Gruber's words express the ordinary person's perspective on something momentous like the trial – contented ignorance and the acceptance of an unjust system. K., unfortunately, isn't satisfied with ignorance and spends the rest of the novel trying to figure out what the heck is going on.
But Juliusstrasse, where it was supposedly located, was flanked on both sides by almost completely identical buildings, tall gray apartment houses inhabited by the poor. (3.4)
K. is surprised by the court's locale. His trial takes him to a lowly neighborhood that he, as a chief financial officer of a bank, wouldn't normally see.
[K.] realized that this was the first clear defeat he had suffered at the hands of these people. Of course there was no reason to let that worry him, he had suffered defeat only because he had sought to do battle. If he stayed home and led his normal life he was infinitely superior to any of these people, and could kick any one of them out of his path. (4.3)
Part of K.'s bitterness comes from the fact that the court seems to be made up of people who are of such humble circumstances that he would normally consider them inferior to himself. So inferior, in fact, that he could "kick" them out of his way. This inhumane attitude backfires when he gets executed by the very same people at the end of the novel.
for a defendant it was reassuring to imagine what limited funds this court must have at its disposal if its offices were located where tenants who were themselves among the poorest of the poor tossed their useless trash. (4.4)
The court's humble surroundings obscure its true power over the individual. The court seeks to reduce everyone to the same level, to take an ambitious career man like K. and reduce him to an ordinary person, like Frau Gruber, his landlady, for example (see Quote #1).
All of them were carelessly dressed, in spite of the fact that most, to judge by their expression, their posture, the style of their beards, and numerous other small details difficult to pin down, belonged to the upper classes […] They never straightened entirely; backs bowed and knees bent, they stood like beggars in the street. (4.7)
These defendants are just a taste of the future that K. can expect. Members of the upper classes like himself, they have been physically reduced to "beggars" during the long course of their trials.
K. […] was too embarrassed that this sudden weakness had put him at these people's mercy. (4.10)
K.'s brash defiance of the court, as at the end of Chapter 2 for example, actually masks his insecurity, as shown here in this quote.
Josef […] you've undergone a total metamorphosis; you've always had such a keen grasp of things, has it deserted you know, of all times? Do you want to lose this trial? Do you know what that means? It means you'll be crossed off. And that all your relatives will be drawn in, or at least dragged through the mud. (6.2)
With his trial, K.'s relationship with what family he has left deteriorates. He forgets his cousin's birthday, and, as this quote from his uncle reveals, K. demonstrates a marked indifference to the effects of the trial on his family.
In the building where the painter lived […] near the wall, there was a gaping hole from which, just as K. approached, a disgusting, steaming yellow fluid poured forth, before which a rat fled into the nearby sewer. (8.20)
Of all the places in the novel, that impoverished slums seem to be the most real. Whereas the novel presents us with generic cathedrals and bank buildings and lodging houses, the slums are presented with great attention to specific, vivid details. Here it seems that the apartment building is actually urinating into the street, a secretion that is so awful that even rats can't stand it. Yuck!
At the bottom of the steps a small child was lying face down on the ground, crying, but it could hardly be heard above the noise coming from a sheet-metal shop beyond the entranceway […] A great sheet of tin hanging on the wall cast a pale shimmer that flowed between two workers, illuminating their faces and aprons. (8.20)
If you want to get all Freudian, you could see the child as a symbol of the way that K. is himself reduced to a child before the court, who is just as indifferent and disapproving of K. as a domineering parent might be. The fact that the child's cries are drowned out by the clamor of the sheet-metal shop, where human beings are reduced to mere "workers," could also be a nice allegory of the way that modern society is indifferent to the individual's needs.
"The only thing I can do now," he said to himself, and the way his steps matched those of the other three confirmed his thoughts, "the only thing I can do now is keep my mind calm and analytical to the last. I've always wanted to seize the world with twenty hands, and what's more with a motive that was hardly laudable. That was wrong; do I want to show now that even a yearlong trial could teach me nothing?" (10.5)
This is perhaps the closest we're going to get to a moral in the story, such as it is. This last scene where K. moves into lock step with his executioners suggests that K.'s "crime" might just have been selfishness or pride.