To elaborate on ideas already suggested, Miss Maudie, in Chapter 22 of To Kill a Mockingbird, speaks, not about those who purport to be Christians, but about those who are truly Christian. For, one of Harper Lee's motifs is the hypocrisy of "the footwashers" and the other holier-than-thou's.
After the trial when Jem remarks,
It's all right to talk like that--can't any Christian judges an' lawyers make up for heathen juries
Miss Maudie replies,
That's something you'll have to take up with your father.
Miss Maudie refrains from commenting because she has faith in humanity. Just as Judge Taylor displayed his Christianity by hiring Atticus as the defender of Tom Robinson, and just as Heck Tate showed fortitude in giving objective testimony, there may appear a juror who breaks from the conventional wisdom of the others. After all, Mr. Cunningham held up the verdict for a while with his doubt. Miss Maudie believes in the heroic struggle, which is always the struggle of a true Christian.
Miss Maudie realized that Jem had been affected deeply by the jury's conviction of Tom Robinson, so after the trial, she called the kids over for some cake. Scout noticed that there were only two little ones--she always baked one for each of the three children when Dill was in town--and she assumed Maudie had forgotten about Dill. But she gave Scout and Dill the small cakes and cut a large slice out of the big cake for Jem. It was her way of showing special consideration for the elder child. Then she had a little talk with the kids. She told them that Atticus was "'born to do our unpleasant jobs for us.'" When Jem showed his dismay for the lack of support of Maycomb's citizens toward his father, Maudie told him that
"We're the safest folks in the world... We're so rarely called on to be Christians, but when we are, we've got men like Atticus to go for us."
Maudie seems to be saying that while many people pretend to be Christians, it's men like Atticus--who rarely attends church but has high moral ideals--who step forward when they are needed the most.
I think that the answer that you are looking for can be found in Chapter 22. Miss Maudie does not exactly say anything about the Christians of the county, but she does say something about what happens when the people of the county are called on to be Christian.
What she says then is that the people of the county are the safest in the world. That is because when they are called on to do something Christian -- something that is hard for them to do -- they have Atticus to do it for them.
She also says that many people in the town feel that way and that this feeling might be a little step towards justice.