What is meant when Scrooge is described as, "No warmth could warm, no wintry weather chill him" ?

Simply put, Ebenezer Scrooge is a cold man. He has a cold heart. He doesn't appear to care about anyone or anything other than his money. As a result, we are told,

"No warmth could warm, no wintry chill could chill him."

This is a use of metaphor. He is so cold, he cannot be warmed. We see him interact with people at the beginning of the story, before the ghosts, where he could have shown empathy, care, and warmth. He does not. We also see where he could be warmed, like with the men who ask him to donate to charity. This is an opportunity for him to be warmed by the struggles of others during the holidays. He is not.

When it says "no wintry chill could chill him," we understand that he is so cold that the winter weather could not possibly make him any colder. He almost seems inhuman.