The source of man's unhappiness is his ignorance of Nature.

If the ignorance of nature gave birth to gods, the knowledge of nature is calculated to destroy them.

Many men without morals have attacked religion because it was contrary to their inclinations. Many wise men have despised it because it seemed to them ridiculous. Many persons have regarded it with indifference, because they have never felt its true disadvantages. But it is as a citizen that I attack it, because it seems to me harmful to the happiness of the state, hostile to the march of the mind of man, and contrary to sound morality, from which the interests of state policy can never be separated.

People have suffered and become insane for centuries by the thought of eternal punishment after death. Wouldn't it be better to depend on blind matter... than a god who puts out traps for people, invites them to sin, and allows them to sin and commit crimes he could prevent. Only to finally get the barbarian pleasure to punish them in an excessive way, of no use for himself, without them changing their ways and without their example preventing others from committing crimes.

Tolerance and freedom of thought are the veritable antidotes to religious fanaticism.

Can theology give to the mind the ineffable boon of conceiving that which no man is in a capacity to comprehend? Can it procure to its agents the marvellous faculty of having precise ideas of a god composed of so many contradictory qualities?

All religious notions are uniformly founded on authority; all the religions of the world forbid examination, and are not disposed that men should reason upon them.