In Synge's Riders to the Sea, natural elements, including the sea, have supernatural qualities. The sea, which has claimed Maurya's husband and five of her six sons, has a supernatural force to it. Religion is powerless to defeat it.
At the beginning of the play, Cathleen, one of the daughters, asks if the priest can stop Bartley, the one remaining son, from going to sea to sell his horse. Nora, her sister, responds:
"I won't stop him," says he, "but let you not be afraid. Herself does be saying prayers half through the night, and the Almighty God won't leave her destitute," says he, "with no son living."
In other words, the priest is powerless to prevent the deaths of both Micheal (the son who dies at the beginning of the play) and Bartley, the son who dies at the end of the play. Instead, the sea claims both of them, and Maurya's prayers cannot defeat the power of the seemingly supernatural sea.
At the end of the play, Maurya says, "They're all gone now, and there isn't anything more the sea can do to me. . . . I'll have no call now to be up crying and praying when the wind breaks from the south." In other words, by the end of the play, it is clear that the power of the supernatural that is invested in nature is more powerful than religion. Maurya has no more reason to pray, as it's obvious that the supernatural can defeat her prayers.