After Reading The Life of Pythagoras

After I read The Life of Pythagoras, I feel that this book make Pythagoras an oracle. Well, most of the contents in this book are all about the God. Sometimes, I don't understand why back to the ancient, there are so many people dedicate in the religion. Isn't human beings important? How come people can live for God not for themselves? All the philosophers advocated piety, to sacrifice for God and so on. Sometimes, I might think that all the ideas were come from human's desire of power and desire of control.