What story elements did the author use to develop the theme?

One important element in O. Henry's, The Gift of the Magi, is his use of allusion.... references to well-known people, places, events, or artistic works. When the narrator describes Della's hair and Jim's watch, he alludes to the Bible: "Had the Queen of Sheba lived in the flat across the airshaft, Della would have let her hair hang out of 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."

In using this allusion, O. Henry accomplishes three things; humor, comparing the couple's gifts to treasures, and a solid foundation for the more serious allusion, which appears at the end of the story..... the moment when Della and Jim are compared to the Magi.