What is the theme or message in the story "The Last Leaf" by O. Henry?

The message that comes through the most powerfully for me is that you should not judge people by their outward appearances or social persona.  In the story, the most gruff character, Behrman, "was a fierce little old man, who scoffed terribly at softness in any one."  And yet it is Behrman that takes the very "soft", compassionate step of painting the leaf, which in essence, saves Johnsy's life.  In a way, he sacrifices his own to save hers.  So we should not judge people by what image they promote, but instead by their actions, because it is, in the end, actions that truly make an impact.