Emile Durkheim argued that the sacred is simply a symbol of the society, linked religion with society as a "mirror" of the society; authored the book “The Elementary Forms of Religious Life”.
Sigmund Freud was an atheist who viewed religion as an "outward manifestation of basic psychological causes," and considered religion to be: an illusion, a form of "wish fulfillment", and a projection of neuroses.
Sigmund Freud also authored several books exploring the nature of religion, including “Totem and Taboo”, saw God or "the Holy" as the reality that stands beyond and behind what we call "religion," identified this "HOLY" as numinous and the "mysterium tremendum fascinans".
Rudolf Otto authored the book “The Idea of the Holy” and considered awareness of the sacred to be at the heart of the human religious experience.
Mircea Eliade authored the book “The Sacred and the Profane”.