The narrator serves an equally important purpose as the reader- they convey the story being told, and dictate what we as readers do or do not know, and even how we are to feel. In Mary Barton, the narrative voice is third person limited, with occasional interjections of first person thought and reflection, the latter of which will be the chief discussion.
The two main schools of thought concerning the first person narrative use are that it is Gaskell herself placing her thoughts in the novel at face value, and the other is the ambiguous narrator quantifying the underlying opinions given throughout the text. I believe it is a mixture of the two, where Gaskell framed her thoughts and opinions in the voice of an unidentified narrator in order to bolster the opinions stated free of bias. This opinion giving is evident throughout the novel, one such example occurs on page 54, with the narrator stating (in the first person) “and I know what is the truth in such matters: but what I wish to impress is what the workman feels and thinks”. Here the narrator states her knowledge of the plight of the lower class, and says that he/she wants to give us as readers the same knowledge. If Gaskell had outright said this from the voice of her own person, it would serve to discredit the opinions of the narrator, rather than strengthen them, because applying a known identity to the narrator also applies what is known about that identity- in this case that Gaskell is a well-to-do and prominent female author who arguably cannot personally relate to the issues the lower class faced outside of her independent philanthropy work.
The general tone of the narrator when discussing the actual lower class members is one that is condescending at best, and assumes with relatively low levels of warrant that the members of the lower class are not actually self aware of their ignorance, but are rather embodied by it. This is evident on page 225, where the narrator claims that “the actions of the uneducated seem to me typified in those of Frankenstein”, where the implication here is that the lower class has basic elements of human life, but nothing more. This condescending tone occurs again with one of the narrator’s calls to action on page 340, where they state that “as you and I, and almost everyone, I think, may send up our individual cry of self-reproach that we have done all that we could for the stray and wandering ones of our brethren”. The interesting pairing of an effective call to action with a patronizing tone may not have been intentional, but the negative consequences of such pairing were avoided by the narrator being ambiguous rather than known. Had Gaskell had truly implemented her own being into the novel, she would have presented herself and her work in a negative light. By using the ambiguous narrator, she was able to hide (for lack of a better term) behind a faceless man, who was able to take all criticism and give all the call to action.