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. 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.
The orchestrations are great too, as they sneak in arrangements of Christmas carols. The orchestral version of "Good King Wenceslas" stands out, as does the instrumental reprise of "Bless Us All" over the shot of Tiny Tim's empty chair.