Why did Granny say that Richard was going to "burn in hell" ?

Ella was whispering the story of Bluebeard and his Seven Wives and telling Richard how it had changed her and made her aware of magical presences....... but Granny heard her and made it very clear that she wanted "none of that Devil stuff" in her house. Richard made the mistake of noting that Ella hadn't been able to finish the story, and even after upsetting his Granny did a foolish thing by telling her he liked it. For that, she told him that he would burn in hell.