"The Gift of the Magi" is a very short story. The author, O. Henry, spends much of the limited space giving a sparing but vivid glimpse of the Youngs' bleak surroundings and financial situation. As such, there's less of a focus on Jim and Della's personalities. While a few basic conclusions can be drawn about them as individuals, there's more attention given to their love and delight in each other as a couple, which the story suggests is the most precious thing in their lives. This is accomplished mainly through humorous wordplay and wry remarks directed to the reader.
Through short, conversational word choice, O. Henry draws readers into Jim and Della's world and suggests that, while their life has real difficulties, it also has a steady undercurrent of warmth. When Della weeps on the couch, the line "life is made up of sobs, sniffles, and smiles, with sniffles predominating" is offered as a kind of cozy aphorism, or a saying about life in general. With this adage, O. Henry doesn't intend a literal statement, but a droll observation that life usually isn't very tragic or very happy, but somewhere in between. The playful alliteration ("sobs, sniffles, and smiles") fits with the lightly sardonic tone, hinting that Della's sorrow won't dominate the entire story.
O. Henry also uses gentle exaggeration when Della is trying to style her newly shorn hair:
She got out her curling irons and lighted the gas and went to work repairing the ravages made by generosity added to love. Which is always a tremendous task, dear friends—a mammoth task.
Here, Della's plight isn't really very serious—her hair will grow back, after all—but it's described in dramatic language, her hair "ravage[d]" and the task of fixing it "tremendous [...] mammoth." Obviously, fixing one's hair isn't literally "a mammoth task," but the exaggerated word choice shows that from Della's loving perspective as Jim's wife, it is a grave task, more important than anything else in the world right now. The author thus invites readers to see that although Della's sacrifice may have been a small, rather silly act in the greater scheme of things, it came from loving motives. In this sense, it fits with the devoted atmosphere of her marriage and is presented as worthy of respect.
Moreover, the story's style is much more whimsical than it is poetic. For instance, Della's shopping trip for Jim's gift is described this way:
Oh, and the next two hours tripped by on rosy wings. Forget the hashed metaphor.
This "hashed" or bungled metaphor signals that the story isn't meant to be taken in an excessively serious, melodramatic light. To put it another way, O. Henry isn't even trying to create a sophisticated tone. What's most important isn't delicate details, but the bigger point that Della loves Jim and shows that by her actions, even when those actions don't look especially pretty.
All in all, the story's brevity and narrowly focused descriptions and actions keep the story moving swiftly toward the concluding twist. The twist—that Jim and Della's mutually sacrificial gifts end up being useless—interrupts the expectation of a conventionally dramatic, romantic conclusion. Yet the wry interjections throughout have signaled that things aren't always what they seem. Though the ending is anticlimactic, it's clear by now that Jim and Della's love is strong and will endure poverty and disappointment.