“Fix reason firmly in her seat, and call to her tribunal every fact, every opinion. Question with boldness even the existence of a god; because, if there be one, he must approve the homage of reason rather than of blind-folded fear. Do not be frightened from this inquiry by any fear of its consequences.... If it end in a belief that there is no god, you will find incitements to virtue in the comfort and pleasantness you feel in its exercise and in the love of others it will procure for you.”
“Because religious belief, or non-belief, is such an important part of every person's life, freedom of religion affects every individual. Religious institutions that use government power in support of themselves and force their views on persons of other faiths, or of no faith, undermine all our civil rights. Moreover, state support of an established religion tends to make the clergy unresponsive to their own people, and leads to corruption within religion itself. Erecting the "wall of separation between church and state," therefore, is absolutely essential in a free society.
We have solved, by fair experiment, the great and interesting question whether freedom of religion is compatible with order in government and obedience to the laws. And we have experienced the quiet as well as the comfort which results from leaving every one to profess freely and openly those principles of religion which are the inductions of his own reason and the serious convictions of his own inquiries.”
“The impious presumption of legislators and and rulers, civil as well as ecclesiastical, who, being themselves but fallible and uninspired men, have assumed dominion over the faith of others, setting up their own opinions and modes of thinking as the only true and infallible, and as such endeavoring to impose them on others, hath established and maintained false religions over the greatest part of the world and through all time: That to compel a man to furnish contributions of money for the propagation of opinions which he disbelieves and abhors, is sinful and tyrannical;...”
“Christianity neither is, nor ever was, a part of the common law.”
“No man complains of his neighbor for ill management of his affairs, for an error in sowing his land or marrying his daughter, for consuming his substance in taverns.... In all these he has liberty; but if he does not frequent the church, or then conform in ceremonies, there is an immediate uproar.”
“The priests of the different religious sects ... dread the advance of science as witches do the approach of daylight, and scowl on the fatal harbinger announcing the subdivision of the duperies on which they live.”
“Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus.”
“Millions of innocent men, women, and children, since the introduction of Christianity, have been burnt, tortured, fined, and imprisoned; yet we have not advanced one inch toward uniformity. What has been the effect of coercion? To make one-half the world fools and the other half hypocrites. To support roguery and error all over the earth.”
“I know it will give great offense to the clergy, but the advocate of religious freedom is to expect neither peace nor forgiveness from them.”
“An equal application of law to every condition of man is fundamental.”
“Rightful liberty is unobstructed action according to our will within limits drawn around us by the equal rights of others. I do not add "within the limits of the law" because law is often but the tyrant's will, and always so when it violates the rights of the individual.”
“...every one must act according to the dictates of his own reason, & mine tells me that civil powers alone have been given to the President of the US and no authority to direct the religious exercises of his constituents.”
Thanks to Positive Atheism for compiling these.