A pure expression of love.
O Henry has done an amazing job at showing people the true meaning of love is sacrifice.
He did add a pinch of romance to this story which had a gray background and this is something we don't see in today's literature.
And the way he ends the story with the lines
' "Dell," said he, "let's put our Christmas presents away and keep 'em a while. They're too nice to use just at present.' Shows us how pure and beautiful sacrifices are.