The Devil, Power, and Benignity

Such strange lingering echoes of the old demon-worship might perhaps even now be caught by the diligent listener among the grey-haired peasantry; for the rude mind with difficulty associates the ideas of power and benignity (page 6).

Does this essentially say that the ignorant and unlearned tend not to associate the quality of power with the quality of kindness or gentleness; that people with power are invariably viewed as cruel or some such thing in the eyes of the ignorant, which results from limited experience? Perhaps in such minds it is inconceivable that a powerful person could be kind, and, conversely, that a kind person have power?

They had, perhaps, heard their fathers and mothers hint that Silas Marner could cure folk’s rheumatism if he had a mind, and add, still more darkly, that if you could only speak the devil fair enough, he might save you the cost of the doctor (page 6)

What does the bolded section mean? Does it mean to speak kindly or fairly of the devil? Note: Page numbers refer to the document page numbers of this pdf.