In To Kill a Mockingbird, what does the symbol about old trees, pillars and old tradition mean?

The old trees in Maycomb and the pillars of the courthouse
stand for the traditions of the Old South, the South prior to the Civil War. In the
novel, Harper Lee describes the pillars of the courthouse as being "too heavy" to bear
their light burden. The original courthouse burned down and a new courthouse was built
around the pillars. This symbolizes that although the Civil War and emancipation
supposedly freed the slaves, it did not eradicate racism and prejudice from the South.
Those attitudes and values were still standing, as represented by the pillars. Such
entrenched values are not easily destroyed, and the pillars foreshadow Tom Robinson's
trial. Even with a wonderful lawyer like Atticus, Tom is still a victim of racial
prejudice and is convicted for a crime he did not commit.