Well, first it is important to realize the full title of the book which is By the River Piedra I Sat Down and Wept: A Novel of Forgiveness. So keep in mind that the divine feminine is strong within this book as well as forgiveness within the confines of paganism.
The novel is mainly about the character of Pilar and her life at university as she struggles for independence. Pilar eventually reconnects with an old flame (from her youth) and this changes Pilar's life. The young man is a guru of sorts with qualities of healing. Even miracles are attributed to him. Pilar and her love decide to travel through the French Pyrenees in order to continue their journey of love and adventure together. It is in one of the villages there, by the River Piedra of the title, that the two lovers unearth and exorcise their demons together.
In conclusion, also realize that this is a journey from Pilar's former religious practices to her "new" spiritual ones once she finds the charisma in her former lover. Paganism is paramount here, but kindness and compassion still are a large part of this vastly spiritual novel.