Miss Maudie makes a comment to the Mennonites as they ride through town in a wagon, getting ready to see the trial of Tom Robinson.
They wore cotton sunbonnets and dresses with long sleeves. A bearded man in a wool hat drove them. "Yonder's some Mennonites," Jem said to Dill. "They don't have buttons." They lived deep in the woods, did most of their trading across the river, and rarely came to Maycomb. Dill was interested. "They've all got blue eyes," Jem explained, "and the men can't shave after they marry.”
The Mennonites shake a Bible at Maudie and quote Scripture:
He that cometh in vanity departeth in darkness!
Miss Maudie answers with another verse:
A merry heart maketh a cheerful countenance.
The point in the story is intolerance. These people, along with the citizens of Maycomb, are outwardly claiming to be Christians, and yet they are riding into town to witness the trial of an innocent black man.
This illustrates three ways that the Mennonites and Amish interpret the Bible to explain living differently than the rest of the world. Their clothing is different, their appearance is different, and they shun the use of modern conveniences.
The Mennonites and the Amish believe the Bible instructs them to live this way, separate and living out their beliefs in their daily lives. The Amish are much stricter than the Mennonites, however, so this instance in the novel is not really true to life. Most Mennonites to not require the dress restrictions in the same way as the Amish.
For example, they don’t force their men to have untrimmed beards or insist that they use hooks and eyes in place of buttons on outer garments. They don’t insist on horse and buggy transportation; horse-drawn implements for farming; plain and distinctive dress patterns; no electricity in homes; shunning, etc.
There are several Bible verses that both groups cite to illustrate this: Peter 2:9: But you are a chosen people, a royal priesthood, a holy nation, a people belonging to God, that you may declare the praises of him who called you out of darkness into his wonderful light (most main-stream Christians believe this verse applies to Israel, however). Another verse is Romans 12:2: Do not conform any longer to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God's will is—his good, pleasing and perfect will. There is also James 4:4: You adulterous people, don't you know that friendship with the world is hatred toward God? Anyone who chooses to be a friend of the world becomes an enemy of God.
I don't believe the Amish or the Mennonites would act in a judgmental way as outlined in this novel, however. Do you remember how the Amish even forgave the madman who killed their children at West Nickel Mines School in Pennsylvania in 2006? You can look it up.