In Chapter 12 of To Kill a Mockingbird, how does Harper Lee shows that racial prejudice is ingrained in Maycomb?help!! help!!! and also, why is...

Chapter 12 marks the children's visit to Calpurnia's
church.  Though most of the parishoners are more than welcoming to the Finch
children, Lula, a "tall Negro woman," makes Scout and Jem feel out of place at the
church.  Lula asks Cal why she has brought white children to the AME Zion church, and
says,

You
ain't got no business bringin' white chillun here--they got their church, we got our'n. 
It is our church, ain't it, Miss
Cal?

When Jem suggests that
they go home because they're not wanted, Zeebo explains that Lula is "contentious
because Reverend Sykes threatened to church her."  It's clear that Lula is well aware of
the racial climate and tensions in Maycomb, and she feels that the Finch children
shouldn't be present at her church. 

The last sentence of
the chapter announces Aunt Alexandra's arrival, and in the beginning of Chapter 13, we
learn that Alexandra has arrived to act as a "feminine influence" in the Finch
household.