“glowing” has connotation of warm and bright which reflects Scrooge’s new character. It also shows that he is radiating happiness and that he cannot keep it all in emphasizing his change.
"I'm as giddy as a drunken man"
shows how happy and carefree he is, and the simile directly contrasts with “Hard and sharp as flint”.
"No fog, no mist"
pathetic fallacy contrasts with the fog in stave 1 and shows that the weather is now bright and warm like Scrooge’s new character.
"As light as a feather"
Religious imagery shows that the weight of negativity has been removed from Scrooge, and he is now free of his sins. Also “feather” could be linked to angels showing he is accepted in heaven.