Realism is a mode of writing that gives the impression of recording or ‘reflecting’ faithfully an actual way of life.
Metafiction adds a layer on top of the realism that gives the effect of a narrator commenting on the realistic effects in the novel.
When a reader reads a metaphysical piece that has an authorial commentary then, if this is done well (with a pleasant authorial voice), it has the effect of lowering the reader’s defences. The reader suspends belief and lets the narrator’s voice inside their head and then believes the things that he/she is being told.
When this happens, the bad is taken in with the good (unless something happens to jolt the reader out of the awareness that they are reading fiction – and a skilful writer will not allow this to happen). Thus it is possible for an author writing with a metafictional style, under the guise of a narrator, to slip immoral notions inside the reader’s mind and to get them accepted. In this way, it is possible to corrupt the mind of the reader.
An intrusive/metaphoric narrator should therefore only use the rhetorical devices (comment, imagery, description, telling, showing) to heighten the effect of the story in a way that enhances life. A writer should keep the fire alive, not snuff it out.