Meaning of this paragraph

[Fear not, only believe]

No, I'm sorry, "for three days" does nothing to make 'cinders' concrete. For three days, he used bitter words to help her realise the 'truth', then he used calming words. "Three days" is probably literal, but it doesn't make 'cinders' literal.
"To have someone on cinders" can be as metaphorical as "to have someone on tenterhooks", and the length of time has no bearing on the figurative use.

Might the three days be figurative - like the resurrection or the older idea of the Harrowing of Hell (cinders) - as she is reborn in a sense?

Now you got me all confused, all of a sudden the idea that he spoke metaphorically looks quite possible to me!
And as for the figurative three days, I don't think it was an allusion to resurrection; at the end of the day, Wigglesworth was quite plain at speaking/preaching, so I don't think there was some hidden meaning behind his words (that's the reason I thought the oil, bitter drugs and cinders were concrete substances in the first place).

But, who knows, this is after all a discussion for native speakers and I can only make suggestions.

[Tdol]

Not at all- you know more about Wigglesworth than we do. I had never heard of the book until this discussion started and am only commenting on the words.