Irony is central to "First Confession," as the narrator portrays his younger self as probably sinful but certainly confused about the meaning of various Catholic sacraments and rites. At age seven, he still views many of the Church’s requirements as unfair impositions made by his family and has little understanding of their spiritual significance. The irony emerges when it turns out that he actually enjoys confession, which he had been dreading, and even looks forward to returning. The first-person narrative, which presents the memories to seem fresh rather than reconstructed, effectively conveys this underlying irony.

Jackie’s family members seem to him put on earth to make him miserable, especially his grandmother. Hearing tales of confession's many negative outcomes, he becomes increasingly apprehensive about making his first confession and his expectation of the upcoming experience is gloomy. The character of the priest, who had been an object of Jackie’s dread, likewise features in the story’s irony. Rather than the distant, foreboding figure that Jackie imagines, he proves to be friendly and empathetic to Jackie’s plight.

Nora, Jackie’s sister, also adds to the irony in the outcome. While her self-identity hinges on occupying a moral status superior to that of her brother, it is she who physically attacks him in the church after he commits the faux pas of falling out of the confessional. With the priest forgives him this lapse and sees her violence, the tables are turned, and the sister loses the moral high ground.