in page 179 of to kill a mockingbird it says “the concrete pillars supporting its south roof were too heavy for its burden”. the pillars could symbolise the fact that the racist people have started to change their minds about whether racism is the right way to do things because it says at the end of the sentence “there burden” the definitions of burden are :

a. Something that is emotionally difficult to bear.
b. A source of great worry or stress; weight
this could mean that empathy has started to affect them due to the fact that they see racism every day in the streets.
in the second paragraph it says “rusty unreliable instrument” this could symbolise how racism is because it will only work when peapole are uneducated.
it could also mean that the world is changing and that people of the old world are trying to hold there world together although there world is unreliable while people  of the new world built the court to spite peaopole who are still trying to hold on to the old world.
the sentence that the pilliars are too heavy for there burden could mean that peopole around that time were less caring about the slaves than in the future.