Why does James Joyce use the technique of epiphany in The Portrait of the Artist as a Young Man?

An epiphany is a sudden, unpremeditated insight into the
essential meaning of an object. The observer perceives in a whole new way extraordinary
beauty and unity in an otherwise ordinary thing. When such an experience appears in a
work of literature, the artist presents it in a symbolic
way.

It is his aesthetic belief which prompts Joyce to
use the technique of epiphany in his written work, particularly in The
Portrait of the Artist as a Young Man. Joyce believed that it was the
obligation of an author to record these fleeting moments of metaphysical beauty. In
Stephen Hero, the first draft of the novel, Stephen explains the
occurence of it thus: Its soul, its whatness, leaps to us from the vestment of its
appearance. The soul of the commonest object...seems to us radiant. The object achieves
its epiphany."

Epiphanies in the novel include Stephen's
otherworldly perception of the young girl wading "in midstream, alone and still, gazing
out to sea...like one whom magic had changed into the likeness of a strange and
beautiful sea creature," and the swallows seen from the steps of the
library.