One of the few joys left to the slaves was their

religion

Explanation:

On their day of rest, the slaves would often escape to the woods for their own service. Sometimes the women would wet quilts and hang them from the branches. This would help muffle the sounds of their service. The slaves' services were lively.

Many of the slaves found their religion gave them a chance to open their hearts and express their deepest longings. Their worship offered them a breath of hope. One of the few joys left to the slaves was their religion

Here is an example of foreshadowing in the story. And you can take this and figure out and explain the use of foreshadowing from this excerpt:

Nadine Gordimer weaves many examples of foreshadowing into "Once Upon a Time." The frame story introduces the concept of fear. The idea of the subterranean mining tunnels that rock the narrator's house—dark, invisible, and cryptic—foreshadow the ethnic unrest that rocks the social fabric of the suburban community in the bedtime story.