Theoretically, our omniscient narrator has no investment in the story, they’re separate and unbiased relating the facts as they are, but this is rarely true. Charles Dickens is well known for showing the plight of the poor in Victorian Britain, he relates the facts but he is not unbiased. However, when he digresses from a story to tell the reader about the suffering of the poor he isn’t breaking perspective because this is the narrator’s perspective. Strictly speaking, although it can be easier to refer to it as such, when we use omniscient narration we’re not in the point of view of any of the characters of the story so if we have the narrator tell us about something that isn’t part of the point of view of the characters they’re not ‘interrupting’ the story as such.
However, like description, we need to remember that while we’re telling the reader about something the forward motion of the story is interrupted. This can be tricky to pull off because we either need to keep it short or have a very engaging authorial voice. In his day Dickens was considered very emotive, although he might appear less so to a modern reader due to changing styles, it’s this emotion that carried the reader through his sections of ‘information’. These days readers are sometimes put off by these sections because, although they give the story context, the story might still be able to function without them. This is part of how we ended up with abridged editions of classics that tend to cut out or trim the informative but not strictly narrative sections. This doesn’t mean we can’t include them but we have to be aware when we’re editing that we need to keep these sections as engaging as the rest of the story. While they might not be part of the narrative they are still part of the story.
Dickens was passionate about social justice so he put it in his stories, it’s generally accepted that in his stories he’s as much trying to educate as entertain his readers. I would say, and this is only my opinion, that he’s trying to make the education as entertaining as the story itself. By the standards of the day, when stories tended to be more wordy, his narrator’s speeches were probably less conspicuous then they are in the present where they have become less common in fiction than they were.
On a side note we can’t say what Dickens definitely intended with his writing we can only interpret what’s on the page, hence why I say ‘generally accepted’. We could argue that in the case of Dickens his intentions are clear, but when we’re analysing fiction we’re interpreting what’s on the page and as we’re not inside the writer’s head we can’t say ‘they definitely meant’. It’s perhaps also important to note that if the writer is still alive and we start telling people ‘this is what they meant’ and it isn’t what they meant then they’ll probably get very annoyed.