For ten seconds let us regard with discreet scrutiny some inconsequential object in the other direction.
The expensive gifts Della and Jim buy are symbolic of their love. The items themselves have very little meaning - in fact, the couple puts them away. The selfless sacrifice that they represent makes them precious.
The end of the story is an example of situational irony. Each character is faced with a circumstance that is the opposite of what they expected. This irony adds a trademark O. Henry's twist to the end of the story.
The narrator intrudes upon the story multiple times. When he draws attention away from the characters and speaks directly to the readers, he is making his presence obvious to the reader, breaking the fourth wall.