Answer:
As a result of their presents being given out of love, the narrator draws the conclusion that Jim and Della are far wiser than the Magi. People who give out of love and self-sacrifice are truly smart because they understand the importance of self-giving love.
Because they recognize that their love for one another and readiness to make sacrifices are more significant and valuable than any financial possessions they may have, Jim and Della, are among the wisest of men.
The selfless love one feels for the other is expressed in those "useless" presents, which makes them very valuable in the end.