This statement accurately sums up the theme of this excellent short story, which has such an unexpected ending as we realise that both Jim and Della sacrificed that which was dearest to them in vain so that they could buy a useless present for the other. Note the way in which Della's hair and Jim's watch are described as being priceless possessions for them:
Had the Queen of Sheba lived in the flat across the air shaft, Della would have let her hair hang out the window some day to dry just to depreciate Her Majesty's jewels and gifts. Had King Solomon been the janitor, with all his treasures piled up in the basement, Jim would have pulled out his watch every time he passed, just to see him pluck at his beard from envy.
Note the way in which the allusions to the Queen of Sheba and King Solomon serve to highlight the value of Della's hair and Jim's watch. Yet these two treasures they willingly give up for love of one another. Although they do buy expensive gifts for each other, the irony of the story is that these gifts are now useless. Yet, in spite of their "foolishness," the narrator himself praises them for how their actions demonstrate that the giving and receiving gifts is much more about the love that is behind it than the gifts themselves:
But in a last word to the wise of these days, let it be said that of all who give gifts, these two were the wisest. Of all who give and receive gifts, such as they are wisest. Everwhere they are wisest. They are the Magi.
The true love that Jim and Della show for each other through their willingness to sacrifice their most precious possession for the other is so much more important than the watch fob and the combs that they gift to each other.