The first time that the narrator’s crush (Mangan’s sister) talks to him is an important moment in the story, as it establishes the depth of his feelings for her. Joyce uses imagery to transform a simple moment between these two characters (they talk for no more than a couple minutes) into a moment of profound, if one-sided, longing:
The light from the lamp opposite our door caught the white curve of her neck, lit up her hair that rested there and, falling, lit up the hand upon the railing. It fell over one side of her dress and caught the white border of a petticoat, just visible as she stood at ease.
By having the narrator notice all these details about where the light hits Mangan’s sister, Joyce does two things. First, he offers visual imagery that pulls the reader closer into the story and allows them to see Mangan's sister through the narrator's eyes. Second, he shows the reader that the narrator is paying close attention to Mangan’s sister’s body, hinting that he is coming into his sexuality for the first time. That the narrator is simply noticing her neck, hair, and the border of her petticoat shows that his gaze is still fairly innocent, even as he clearly desires to be closer to her, indicating that this is his first experience of young love.
Up until this point, the narrator has been watching Mangan’s sister through his window “morning after morning,” but only from far away. Joyce effectively uses imagery to highlight the importance of this moment that the narrator gets his first look at her up close and begins to long for her even more deeply.
In the final lines of “Araby,” the narrator describes his internal experience using imagery:
Gazing up into the darkness I saw myself as a creature driven and derided by vanity; and my eyes burned with anguish and anger.
The narrator has just failed to purchase an exotic gift from the market for his crush (Mangan’s sister) and, alone in the dark, closing-down market, experiences his shame both visually and viscerally, allowing readers to do the same. He sees himself as a “creature”—denoting how this failed endeavor makes him feel less-than-human—and also describes how his eyes “burned with anguish and anger,” allowing readers to remember moments their eyes burned in similarly desperate situations.
The intensity of the imagery allows readers to understand that this is a critical moment in the story—the narrator did not merely lose the opportunity to purchase a gift for his crush from the market, he also lost his sense of optimism and possibility. All of his hopes for escaping the harsh circumstances of his working-class Dublin conditions—via the excitement of young love and the enchantment of an “Eastern” marketplace—have been squandered. He has come of age but has lost his innocence in the process, concluding that he let his “vanity” get the better of him. The narrator’s use of the phrase “driven by vanity” here also suggests that he may be viewing this experience through a religious lens, judging himself for seeking escape via secular (and sexual) means.
