I would want to answer this question by focusing on setting, and in particular the description we are given on the bazaar and how it compares to the fevered imagination of the narrator in terms of what he expected the bazaar to be like. This of course is one of the central conflicts in the story--the conflict between the romantic expectations and illusions of the boy and the harsh reality of life--and the setting of the bazaar helps trigger the epiphany that resolves this conflict.
Note the way that the narrator imagined the bazaar before he went there. Combined with the idea that he is a knight-errant on some noble quest for his true love, the bazaar is imbued with magical enchantment:
The syllables of the word Araby were called to me through the silence in which my soul luxuriated and cast an Eastern enchantment over me.
The word "Araby" seems to act like a charm on the narrator, which he likens to an "Eastern enchantment." Yet, when he arrives at the bazaar, after travelling in a "bare carriage" and descending on an "improvised wooden platform," the banality of the bazaar is evident. Note the description of the bazaar we are given when the narrator enters:
I passed in quickly through a turnstile, handing a shilling to a weary-looking man. I found myself in a big hall girdled at half its height by a gallery. Nearly all the stalls were closed and the greater part of the hall was in darknes. I recognised a silence like that which pervades a church after a service.
Araby is actually dark, silent and ominous, and the only voices the boy can hear are those of two young women speaking in English accents about some trivial gossip. The irony is evident as the bazaar is nothing like the boy imagined it to be, just like his romantic dreams and illusions in reality are nothing, which triggers the epiphany in the final paragraph.
The boy’s biblical and holy descriptions of the setting and Magan’s sister enhance his sacred adoration toward her which ultimately leads him through maturation from a boy to a man. To the boy, the girl is saintly and angelic; she is always surrounded by “light”, as if by a halo. She becomes an object of faith to the boy and when she finally talks to him the light “[catches] the white curve of her neck, [lights] her hair… [and] the hand”. When she tells him how she wishes to go to the Araby, he promises he will “bring something back”. He imagines himself as a knight in search of the Holy Grail and his trip to the Araby is to him a holy crusade. The bazaar is filled with “darkness” and “silence” which he describes as an enchanted “church after a service”. Yet, as the Holy Grail was never found, the boy realizes at the bazaar that his love is not to be found. Through such realization, the boy takes his first step to adulthood.