Imagery in The Devil and Tom Walker
Throughout the tale Irving uses imagery to show both Tom’s inner corruption and remind the audience of his damnation. For example, images of fire or sparks remind the reader that Tom’s soul will suffer from the flames in hell.
Simply having the Bible around the house doesn't help hypocrites like Tom when the devil comes knocking at his door. Irving captures this idea perfectly by having the Bible buried under the land jobber's mortgage that Tom is about to foreclose, revealing Tom's real priorities.
While horse's shoes can make sparks when they hit the pavement, the image of fire from this action reinforces the demonic nature of the steed and the eternal hellfire and damnation Tom is going to suffer.