The Prioress is important to The Canterbury Tales because she is one of the only devout people on the pilgrimage, one of the only people actually going on the pilgrimage to worship. Though Chaucer's description of her in the General Prologue is rather unflattering, her tale attests to her true piety. 

The Prioress's Tale is about a young boy who sings constant praise to Mary. The evil Jews in the land hate the boy's singing and hire someone to kill him. His throat is slit, and he is thrown into a cesspool. Although the boy is dead, he continues to sing praises to Mary until his burial. He says Mary placed a pearl on his tongue and instructed him to do so. When a priest removes the boy's tongue, the boy ceases his singing and is buried peacefully. The priest declares him a martyr, and the Jews who murdered him are all killed. 

The Prioress, who also venerates Mary, tells a highly religious tale. While other tales are full of sex, debauchery, and sin, the Prioress's Tale is about righteousness, faith, and worship. Furthermore, the tale attests to the faith and power of young, poor people, as they are the ones who have the strongest relationships with holy people. The Prioress's character reflects idealized religious beliefs as well as common cultural beliefs (i.e. that Jews are evil and Mary should be praised).