Understanding the Main Idea of 'The Gift of the Magi'

In the brief story titled 'The Gift of the Magi' by O. Henry, a young couple, Jim and Della, are very much in love but are struggling financially. As Christmas approaches, both want to buy a special gift for one another but each has only a small amount of money. Della decides to sell her beautiful long hair to buy a platinum chain for Jim's prized possession, his watch. Unbeknownst to her, Jim sells his watch to buy Della a set of combs for her hair. When they exchange gifts, they realize the irony of their sacrifices but also the depth of their love.

What is the main idea of this story?