Many would argue that they were incredibly foolish to give up that which was most precious to them. Delia loved her hair and it was renowned as being quite beautiful. Jim was very proud of his watch and it had been handed down through his family so it wasn't something to be sold lightly. So on the surface, their exchange was foolish as they ended up with, practically speaking, useless gifts.
Of course the wisdom of their exchange was that it showed such great love for the recipient of the gift. A young couple, struggling to make ends meet sacrifice everything for each other, likely demonstrating a commitment and willingness to sacrifice that will see them through any kind of tough times together. Perhaps this is why they are later said to have been so wise.
Della and Jim endeavoured to translate their fathomless love, which is a spiritual attributes, into material representation. For this rash enterprises they are called foolish. Neither of their sacrifices proves prolific from the materialistic point of view.
If Della and Jim wanted to prove as to what extent they could go for the sake of their exposures of love, they, undoubtedly, came out with flying colours. At least in this respect they are the "wisest".
In the worldly sense Jim and Della are foolish for many reasons .First of all , the depth of their love does not commensurate with means of lively-hood .They do not mind to know each other’s choice of Christmas gift .Each beyond the others knowledge sells away the highest treasure .
In the concluding part of the story, the narrator calls them wisest. The approval coincides with the meaning of Christmas gift .It is not exchangeable .It comes from heart as the symbol of love .It can not have any material value .It is as great as Christ Himself .Its trace comes in feeling only when one becomes empty of material –possessions .
They are referred to as two foolish children because they are married and poor. They are also impulsive in their purchase of the gifts and don't ask each other if that is something they would truly want.
This being said, I believe that they are more wise that many people. They demonstrate the true depth of what the Christmas holiday was all about. The idea of giving the perfect gift just as Christ was the perfect gift given to mankind.
They are unselfish and dedicated to one another. Perhaps young love may seem foolish, but it is innocent and filled with promise.
The three wise men from the East brought gifts out of reverence. They were rich enough to present gold which, by no way, tell upon their stock of pelf. But, Jim and Della parted with their most precious possessions just in order to display the farthest extent that they could rush for the sake of love, no matter, if the return would prove materialistic .