O. Henry was very good at describing interior settings. In "The Gift of the Magi" he presents a fairly thorough description of the furnished flat in which Jim and Della live. However, O. Henry knows that lengthy descriptions tend to be dull. They slow down the dramatic action. So it is observable in this furnished flat, in which almost all the action takes place, the description of the interior is broken up and interspersed with the action, rather than being presented and disposed of in one solid block of prose. For instance, there is a separate description of the pier glass in which Della looks at herself. A pier glass is a long and narrow mirror. This one is so old that it has probably lost some portions of the shiny substance which creates the reflection. Here is part of O. Henry's description of the pier glass.
Perhaps you have seen a pier-glass in an $8 flat. A very thin and very agile person may, by observing his reflection in a rapid sequence of longitudinal strips, obtain a fairly accurate conception of his looks. Della, being slender, had mastered the art.
When Della realizes that she hasn't been able to save enough money throughout the whole year to buy her husband the kind of Christmas present she feels he deserves, she bursts into tears. This gives O. Henry an opportunity to describe another feature of this dismal dwelling.
There was clearly nothing to do but flop down on the shabby little couch and howl. So Della did it.
O. Henry is furthering the dramatic action and at the same time adding another dash of color to his description of this place that Jim and Della call home. We can almost feel the prickly mohair fabric of that shabby little couch and smell the accumulated dust of decades, just as Della can feel and smell them with her face buried in one of the lumpy cushions. O. Henry must have gotten his characteristic style of mixing pathos and humor from the great Charles Dickens. Like Dickens, O. Henry can describe the most deplorable scenes with an aura of humor and sympathy. This kindly humor is what makes him a superior author and preserves his memory.
Another bit of description added to a bit of dramatic action is the following:
Once she faltered for a minute and stood still while a tear or two splashed on the worn red carpet.
We can picture that worn red carpet with the red dye gradually fading to brown and the nap showing through where foot traffic had been highest. When Jim gets home from work that evening, Della has started some preparations for their dinner.
At 7 o'clock the coffee was made and the frying-pan was on the back of the stove hot and ready to cook the chops.
It would appear that this so-called flat does not have a separate kitchen, and may not even have a separate bedroom. We can smell the lingering odors of all the meals this couple has eaten in their one-room flat. They live in a building that used to be a private mansion and, like so many others in Manhattan, was converted into rental units.
In the vestibule below was a letter-box into which no letter would go, and an electric button from which no mortal finger could coax a ring.
O. Henry had undoubtedly lived in many such places himself. He seems to have taken great pleasure in describing buildings which were once quite grand but have slowly and inexorably deteriorated over the years and will eventually have to be torn down to make way for office buildings or luxury apartment houses. His description of the run-down former mansion in his story "The Furnished Room" is even better than his description of Jim and Della's little flat in "The Gift of the Magi." O. Henry uses a somewhat larger canvas to paint a picture of Greenwich Village, the artists' colony, in his story "The Last Leaf." People have to live in these places, so the action, dialogue, and description are all skillfully intermingled. The furnishings are not separate entities but intimate parts of the occupants' lives.