In "Araby," what does Mangan's sister do to make a trip to the bazaar so important to the narrator?

Mangan's sister doesn't
need to do anything special to make the trip to the bazaar important to the narrator. He is so
enamored of her that the fact that she simply speaks to him about the bazaar would probably be
enough to make him want to go. He says,

At last she spoke
to me. When she addressed the first words to me I was so confused that I did not know what to
answer. She asked me was I going to . I forgot whether I answered yes or no. 
It would be a splendid bazaar; she said she would love to go [....]. She could not go, she said,
because there would be a retreat that week in her convent [....]. 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.

Not only does
the narrator hope to make her happy by bringing her a gift from the exotic Araby, but he
describes her appearance as though she were magic, lit up, and purely beautiful. Even before she
speaks to him, he thinks of himself as her champion, a hero. Just prior to their conversation,
he says, "I imagined that I bore my chalice safely through a throng of foes. Her name
sprang to my lips at moments in strange prayers and praises which I myself did not
understand." When Mangan's sister mentions her disappointment that she cannot go to the
bazaar, she, in essence, gives him his quest.

I disagree, incidentally, that
the narrator's failure to name her means that his childhood feelings for her were, in fact,
silly or childish. He is unnamed as well. As the other commenter states, this is a coming-of-age
story, and the narrator does lose his innocent naivety, but the namelessness of both himself and
his childhood love serve to make this story feel more universal.