Through a rigorous research work, this book explores the fascinating universe of the sacred to unveil the how of religions and delves into the meaning they have for the human being since the beginning of time. What was the first religion of mankind? How did the notions of God, sacrifice, salvation, prayer, clergy ...? Why was it passed from worship to female deities to male ones? From the belief in many gods to only one? Who are the founders of the great traditions and what are their messages? Why is violence commonly related to the sacred? What are the similarities and fundamental differences between religions? These questions, among many others, concern many of our contemporaries. Likewise, in a world in which religions mix and collide, it is necessary that both believers and non-believers understand the religious phenomenon.