There are several instances of intrusion, or the insertion of the author's point of view, in A Christmas Carol. Although not as common today, author intrusion was considered quite common and acceptable during the time period that Dickens wrote.
The novel begins with one such intrusion in Stave 1 as Scrooge questions the wording of a common simile.
In Stave 2 there is a brief, yet very well-known, example when Dickens describes the proximity of the Ghost of Christmas Past to Scrooge: "as close to it as I am now to you, and I am standing in the spirit at your elbow." Stave 2 goes on with a more lengthy intrusion during the observation of Belle, Scrooge's ex-fiancee, with her husband and daughter.
These are just three examples throughout the novel, and they are part of the reason that Dickens' works can be such a struggle.