In the story The Gift of the Magi how does O. Henry uses irony to develop the theme of the story?

In the story The Gift of the Magi O.
Henry uses irony to develop the theme of the story by presenting us with two characters
who are described as "silly" or "foolish", because they are young, in love, and living
life with financial difficulties during the holidays: A time where everyone is bit by
the fever of gifting, and buying things for others.

Within
this context we get the biggest irony of all: They cannot find the way to please each
other during the season, and their love for each other makes the other sacrifice things
they like for the sake of making the other happy. In the end, they gave each other the
same thing they sacrificed.

All this is a lesson on
altruism and the things one does for love. It is a lesson also on how sacrifices become
small when one does them for the right cause, and how getting things becomes unimportant
in relationship to the happiness that they provoke in someone we
love.