Consider “Sweat” a moral tale, one meant to teach a moral, a lesson, one that pits Good against Evil. In this moral tale, what can the reader take away from the reading?

At the end of “Sweat,” Sykes is killed by the very snake that he let loose to terrify Delia. Both Sykes and the snake represent Evil, and Delia represents Good. In this respect, the moral of the story is very straightforward: Good triumphs over Evil. However, Zora Neale Hurston also shows that Delia is aware of her husband’s plight while he is still alive and does not try to help him. Thus, she complicates the story by making the contrast a little less tidy.
Hurston strongly foreshadows the end with Delia’s prediction:

Whatever goes over the Devil’s back, is got to come under his belly. Sometime or ruther, Sykes, like everybody else, is gointer reap his sowing.

“As you sow, so shall you reap” is from the Bible. Hurston strengthens the serpentine analogy by using a metaphor that resembles a snake’s motion in curving around a body. The Serpent is the original Biblical symbol of Evil and Satan, so her use of a rattlesnake fits perfectly with a Judeo-Christian themed morality tale.
Delia, although she has some individual characteristics, is not quite three dimensional. She is martyr-like with her hard work and suffering at Sykes’ hands. When she does assert herself, becoming more human than saintly, the story’s plot also becomes more obviously crafted fiction and less like a morality tale. Although the reader is satisfied that Sykes did indeed reap what he sowed, Delia played a hand in influencing the outcome. In her last actions, or lack thereof, she usurped divine prerogative in exacting vengeance.