De rerum natura

Opening of Pope Sixtus IV's 1483 manuscript of De rerum natura, scribed by Girolamo di Matteo de Tauris

De rerum natura ... The Nature of Things, written by Lucretius, using Atomism to dismiss the need of god(s) in explaining how reality works, is both revolutionary and courageous as said poem was written around 56 BC when Roman Gods ruled society without question.

De rerum natura, written by the Roman poet Lucretius.

Lack of divine intervention

After the poem was rediscovered and made its rounds across Europe and beyond, numerous thinkers began to see Lucretius's Epicureanism as a "threat synonymous with atheism.

Repudiation of immortality

De rerum natura does not argue that the soul does not exist; rather, the poem claims that the soul, like all things in existence, is made up of atoms, and because these atoms will one day drift apart, the human soul is not immortal. 

Physics

Lucretius maintained that he could free humankind from fear of the deities by demonstrating that all things occur by natural causes without any intervention by the deities. 

When thinking about this work done over 2000 years ago, it's astounding religion, in all forms, continues to rule large parts of civilization without exception.

And so it goes - K. Vonnegut