Miss Maudie means that the Bible can be harmful when someone uses its content for evil. Even though the Bible is meant to inspire hope and love in modern Christian theology, people can twist its words in a negative way and use it to justify negative actions. Alcohol, on the other hand, was often seen as a negative; but it is all about the person using it, Miss Maudie says.
Miss Maudie is explaining to Scout what she knows about the Radley family. Scout is curious about Arthur "Boo" Radley, a shut-in who Scout, Jem, and Dill wonder about all summer. Miss Maudie knew him as a child and explains that his family was very religious. They belonged to a type of Baptist group that Miss Maudie calls "foot-washing Baptists." They believed that every type of pleasure was sinful.
Miss Maudie tells Scout:
"Wasn’t talking about your father," she said. "What I meant was, if Atticus Finch drank until he was drunk he wouldn’t be as hard as some men are at their best. There are just some kind of men who—who’re so busy worrying about the next world they’ve never learned to live in this one, and you can look down the street and see the results."
In this way, she is explaining how Boo Radley's father twisted the Bible's messages and made his home a sad one.