How are Della and Jim poor in material things, but rich in love?O. Henry's "Gift of the Magi"

There is a saying, "The most important things are not
things."  Truly, this saying is applicable to the characters of Della and Jim, who,
though they possess few material things, are indeed rich in the important things of
life.  Living in an apartment in New York that is somewhat rundown as
the

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'Dillingham' had been flung to the breeze during
a former period of prosperity when its possessor was being paid thirty dollars a week. 
Now, when the income was shrunk to twenty dollars, the letter of 'Dilllingham' looked
blurred, as though they were thinking seriously of contracting to a modes and unassuming
D

Della
must sell her luxuriant hair in order to have enough money to purchase a watch chain for
her husband; similarly, Jim must sell his watch in order to purchase the lovely combs
for Della's beautiful hair.  But, in the act of selling their prized possessions, the
young "foolish children" of O. Henry's narrative exhibit such unselfish motives and
genuine love for their spouses that the narrator feels compelled to intrude upon the
narrative and  announce that Della and Jim are the wisest of all--they are the Magi. 
Therefore, they are rich in love, one of those "important things" that "are not
things."  They are rich in knowledge that the other loves him/her.  For, there is no
greater love than charity, according to Christiandom.