This line comes from Chapter 6 of To Kill a Mockingbird by Harper Lee. After the children have decided to peep into the window of the Radley's house on Dill's final night in town, Mr. Radley discovers them and appears in the shadows. As Jem and Dill run, a shot rings out, causing Jem to catch his pants on the barbed wire of the Radley fence. Of course, the shot brings out the other residents in the area. Mr. Nathan Radley stands with a broken shotgun across his arm; Atticus and Miss Maudie, Miss Stephanie Crawford, Miss Rachel, and Mr. Avery form a group as the children sidle near them. When Atticus asks the children what they were doing and where Jem's pants are, Dill explains that he has won them in a game of strip poker. When he says this, Miss Maudie "went off like the town fire siren":
"Do-o-o Jee-sus, Dill Harris! Gamblin' by my fishpool? I'll strip-poker you, sir!"
Intervening, Atticus asks if they were all playing cards. Jem "fielded Dill's fly with his eyes shut," saying that they were playing with matches, instead. Scout comments that she admires her brother's quick thinking because "Matches were dangerous, but cards were fatal." Atticus responds by saying that he does not want to hear of poker in any form, underscoring Scout's thinking that matches are much more harmless.
This attitude reflects one of the culture of the Bible Belt in which Maycomb, Alabama, is part. Gambling and drinking are serious sins that lead to the destruction of individuals and families, according to the Calvinistic/Baptist beliefs. To this day, Alabama refuses to allow lotteries and casinos in the state. (There are Indian casinos, but these are controlled by the federal government.)