Scrooge - [BEFORE][S1] "Once upon a time" | "It was cold, bleak biting weather: foggy withal""
Fairy tale starting is to indicate to the reader to suspends their disbelief as to the fantastical elements of the story, in order that they benefit from the moral message.
Pathetic fallacy. Christmas eve is supposed to be a joyful and loving time yet Scrooge treats it as any other day of the year. Foreshadows dark events that may take place.