In "First Confession," the author uses Irish dialect to set the characters in the particular culture in which the story takes place and also for humorous effect. For the story to have maximum impact, it is important for readers to understand the crucial roles that Catholic sacraments such as confession and Communion play in Irish culture. Additionally, the dialect is familiar to many readers who have listened to Irish actors in films and on TV.
The narrator of the story is a seven-year-old boy named Jackie, who is about to make his first confession. However, he has been taught by teachers and family that he will burn in hell if he doesn't confess all his sins, and recently he has been daydreaming of killing his grandmother and has threatened his sister, Nora, with a bread knife. He goes to church terrified that he will be "given up to eternal justice." After some misadventures climbing around in the confessional, he confesses his thoughts and misdeeds to the priest. Instead of being condemnatory, though, the priest is sympathetic, lets him off with some light prayers, and even gives him some candy.
O'Connor uses dialect subtly, mainly by shortening words, rearranging sentences, and adding a few words of Irish slang, so that readers will still be able to easily understand it. Examples of shortened words include using "twas" instead of "it was" and "tis" instead of "it is." An example of a sentence rearranged to reflect Irish usage is the following: "Was it coming to confession you were, my poor man?" An example of Irish slang is the word caffler; Nora calls Jackie a caffler more than once, and the term is used to refer to a young person who is rather roguish.
The dialogue serves to immerse readers in the conservative Irish Catholic culture in which the boy has been raised. It also helps to bring out the personalities of the characters. Nora, Jackie's older sister, is the person who uses the derogatory term caffler, so we see her as somewhat mean and vindictive. The priest displays his background by using uniquely Irish sentence structure. Jackie uses shortened words to display his timidity and fear before the priest. This all makes the characters seem more real and heightens the humorous aspects of the story.