hard and sharp as flint
adjective "hard" suggests he lacks warmth, empathy and compassion. adjective "sharp" suggests pain - he has no mercy towards others. The simile of "flint" could foreshadow there is a spark of warmth within scrooge.
solitary as an oyster
"solitary" emphasises that he chooses to isolate himself from others. "oyster" scrooge has tough exterior, closing him off to others simile of "oyster" could suggest there is more to be found within (like a pearl)
solitary child, neglected by his friends
"solitary" reminder of the previous simile used. again scrooge is alone but this time not by choice. the juxtaposition of "neglected" and "friends" invoked sympathy
i am as light as a feather
he has cast of the chains of his earlier life "feather" connote of freedom and flight
i am as happy as an angel
closer to heaven contrast to previous adjective "sinner" he has become a better person
tell me if tiny tim will live
"tell me" is imperative showing the reader scrooge generally cares about tiny tims future
External heat and cold had little influence on Scrooge
pathetic fallacy to reveal the character of Scrooge and show the lack of influence the weather had upon him