The missionary ladies are stereotypes. They are presented as a group for the purpose of emphasizing the hypocrisy that is so much a part of this novel. The ladies have been discussing the plight of "those poor Mrunas" (indigenous people supported by their church) and how wonderful it is that Christian people have sent missionaries there (J. Grimes Everett) to lift them from their squalor. Simultaneously, however, they show their racism towards the blacks in their own town. This is a great quote that says it all:
"Mrs. Merriweather faced Mrs. Farrow: "Gertrude, I tell you there's nothing more distracting than a sulky darky. Their mouths go down to here. Just ruins your day to have one of 'em in the kitchen. You know what I said to my Sophy, Gertrude? I said, 'Sophy,' I said, 'you simply are not being a Christian today. Jesus Christ never went around grumbling and complaining,' and you know, it did her good. She took her eyes off that floor and said, 'Nome, Miz Merriweather, Jesus never went around grumblin'. I tell you,
Gertrude, you never ought to let an opportunity go by to witness for the Lord."
In this case, they are referring to the outcome of the trial, in which Tom Robinson was convicted in spite of Atticus' brilliant defense. The blacks in town were not happy about the outcome and were "sulking" about it, as she says.
Note the irony in this quote:
"Hypocrites, Mrs. Perkins, born hypocrites," Mrs. Merriweather was saying. "At least we don't have that sin on our shoulders down here. People up there set 'em free, but you don't see 'em settin' at the table with 'em. At least we don't have the deceit to say to 'em yes you're as good as we are but stay away from us. Down here we just say you live your way and we'll live ours. I think that woman, that Mrs. Roosevelt's lost her mind-just plain lost her mind coming down to Birmingham and tryin' to sit with 'em. If I was the Mayor of Birmingham…"
The ladies are criticizing the northerners (like Eleanor Roosevelt) for being hypocritical towards blacks, claiming that THEY (the missionary women) are superior because at least they are up-front and honest about the way they treat blacks, even if it is with prejudice.
Miss Maudie is watching all of this with disdain. She makes many curt comments to let the ladies know she does not agree with their views. When Mrs. Merriweather tells the ladies about a conversation she had with Brother Hutson regarding blacks, Maudie replies:
"His food doesn't stick going down, does it?"
The missionary ladies also serve as a foil to Scout's character - a tomboy in the midst of genteel ladies. They ask Scout if she wants to be a lawyer when she grows up. She replies she wants to be a lady, and Miss Stephanie Crawford says:
"Well, you won't get very far until you start wearing dresses more often."
Also look at the description of the ladies at the beginning of chapter 24 - they wear hats just to go across the street, they all wear the same color lipstick, etc.
You can find many additional examples in this chapter.