1. Letter to Ezra Styles (June 25, 1819):
I am not [a Calvinist]. I am of a sect by myself, as far as I know. I am not a Jew, and therefore do not adopt their theology, which supposes the God of infinite justice to punish the sins of the fathers upon their children, unto the third and fourth generation; and the benevolent and sublime reformer of that religion has told us only that God is good and perfect, but has not defined him. I am, therefore, of his theology, believing that we have neither words nor ideas adequate to that definition. And if we could all, after this example, leave the subject as undefinable, we should all be of one sect, doers of good, and eschewers of evil. No doctrines of his lead to schism. It is the speculations of crazy theologists which have made a Babel of a religion the most moral and sublime ever preached to man, and calculated to heal, and not to create differences. These religious animosities I impute to those who call themselves his ministers, and who engraft their casuistries on the stock of his simple precepts. I am sometimes more angry with them than is authorized by the blessed charities which he preaches.
2. Letter to Benjamin Waterhouse (June 26, 1822):
The doctrines of Jesus are simple, and tend all to the happiness of man.
1. That there is one only God, and he all perfect.
2. That there is a future state of rewards and punishments.
3. That to love God with all thy heart and thy neighbor as thyself, is the sum of religion.
These are the great points on which he endeavored to reform the religion of the Jews. But compare with these the demoralizing dogmas of Calvin.
1. That there are three Gods.
2. That good works, or the love of our neighbor, are nothing.
3 That faith is every thing, and the more incomprehensible the proposition, the more merit in its faith.
4. That reason in religion is of unlawful use.
5. That God, from the beginning, elected certain individuals to be saved, and certain others to be damned; and that no crimes of the former can damn them; no virtues of the latter save.
Now, which of these is the true and charitable Christian? He who believes and acts on the simple doctrines of Jesus? Or the impious dogmatists, as Athanasius and Calvin? Verily I say these are the false shepherds foretold as to enter not by the door into the sheepfold, but to climb up some other way. They are mere usurpers of the Christian name, teaching a counter-religion made up of the deliria of crazy imaginations, as foreign from Christianity as is that of Mahomet. Their blasphemies have driven thinking men into infidelity, who have too hastily rejected the supposed author himself, with the horrors so falsely imputed to him. Had the doctrines of Jesus been preached always as pure as they came from his lips, the whole civilized world would now have been Christian. I rejoice that in this blessed country of free inquiry and belief, which has surrendered its creed and conscience to neither kings nor priests, the genuine doctrine of one only God is reviving, and I trust that there is not a young man now living in the United States who will not die an Unitarian.
3. Letter to William Short (April 13, 1820):
The Presbyterian clergy are loudest; the most intolerant of all sects, the most tyrannical and ambitious; ready at the word of the lawgiver, if such a word could be now obtained, to put the torch to the pile, and to rekindle in this virgin hemisphere, the flames in which their oracle Calvin consumed the poor Servetus, because he could not find in his Euclid the proposition which has demonstrated that three are one and one is three, nor subscribe to that of Calvin, that magistrates have a right to exterminate all heretics to Calvinistic Creed. They pant to re-establish, by law that holy inquisition, which they can now only infuse into public opinion.
4. Letter to John Adams (April 11, 1823):
I can never join Calvin in addressing his god... his religion was Dæmonism. If ever man worshipped a false god, he did. The being described in his 5 points is not the God whom you and I acknowledge and adore, the Creator and benevolent governor of the world; but a dæmon of malignant spirit. It would be more pardonable to believe in no god at all, than to blaspheme him by the atrocious attributes of Calvin.