One of the reasons this film is so well-remembered. Not only are the sung portions generally great, but the instrumentals tend to be amazing too, especially the music that accompanies Christmas-Yet-To-Come.
Not only are the songs awesome, but several (most notably the Marley Brothers' number) feature actual Dickensian prose worked into the lyrics.
The Cratchet's Christmas Dinner Grace is sung as a hymn blessing the house and its inhabitants. It's a simple little piece, but it conveys all the love the family shares.