What is the significance of the tale of the village of Auchtermuchty?
This tale-within-a-tale almost comes out of the blue, and does not really reveal much in terms of the larger questions at hand. However, there is more beneath the surface than first appears. It resembles a parable and thus resembles the Bible; it is also unique for the multiple layers of audiences who hear the central sermon: the villagers, Robin Ruthven, the witch Lucky Shaw, Samuel Scrape, Robert, and finally the reader. The readers must be more dynamic about responding to the sermon than the gullible townspeople, and must work to see its value as a source of potential insight. It may be oral and it may be a folktale, but it is important nonetheless. Robert ignoring its overall message is certainly inadvisable.
What is the danger posed by Gil-Martin and Robert's fanaticism?
As religious fanatics, Gil-Martin and Robert take their views on the infallibility of the elect and the concept of predestination to extreme ends: they interpret their status as members of the elect as one that confers upon them the inability to ignore moral law, and to commit depraved acts even if they are seemingly against the Scriptures because they cannot be punished or lose their salvation. These fanatical views are also indicative of unease with modernity, and are a way to promote an excessive communality with people who share the same rigid views. Fanatics value private revelation and the erasure of difference. They are an extreme parody what Adam Smith says in his Theory of Moral Sentiments is the key to forming bonds with members of a civil society: sympathy. Sympathy mediates the boundaries of self and the other, but in Hogg, as Ian Duncan writes, "Gil-Martin's 'chameleon' art hijacks the Scottish Enlightenment ethos of sympathy with the techniques of physiognomy, the 'science' [...] of discovering people's inward character by interpreting their facial forms and expressions."
What is the significance of the corpse, and of its being "preserved" or mummified?
When Robert's corpse is dug up, the Editor marvels at how well preserved it is, and indeed, it is even brought up into a sitting position, which makes it look more lifelike. It is thus suspended between life and death, which critic Magdalene Redekop notes is a metaphor for the "life-in-death of Wringhim's confession." There is a sense, though, of decay and mortality in the grave, as well as a lack of permanence, that "mocks the desire to see life as a contained pattern." We as readers want to exhume, want to excavate, and want to put the pieces together of the story in the same way that the grave robbers and Editor want to put physically put together pieces of the body and metaphorically put the pieces together to come to a conclusion about the manuscript's meaning.
What/who is Gil-Martin?
Gil-Martin's identity is one of the great mysteries of the text. He very well could be the devil, with supporting evidence including the fact that he does not pray, he does not admit to having a "Christian" name, encourages Robert to do the most dastardly things, and he shows no sign of repentance. Furthermore, the supernatural aspects such as his ability to change his countenance and his knowledge of people's thoughts and whereabouts combine with his general slyness and manipulation to heavily suggest that he is Satan. However, Robert is obviously mentally ill to at least some extent, and Gil-Martin may be a manifestation of his twisted psyche. Everything Robert says could be probed and found to be something he hallucinated or lied about. The Editor's narrative is less easy to pick apart, but many things can be explained away by coincidence or mistakes of the senses. Thus, we do not know who or what Gil-Martin is, but that lends itself to the book's allure.
Why does Hogg include himself as a character?
This question has interested critics for some time. First, he was keen on having the text be anonymous, and this would be a sort of legerdemain. Hogg had been writing for Blackwood's for a while, and often penned humorous lies and hoaxes. Here, depicting himself as the Shepherd others liked to see him as, he "reclaims the folk identity with which he had begun his career: seizing it back from the Blackwood's wits," as Ian Duncan writes in the introduction to the novel. Duncan adds that, unfortunately, this also means this Shepherd cannot be the writer of the memoir, and the joke turns against him. It was personal for Hogg, not just a humorous joke.