Thomas Paine: Profession of Faith, from The Age of Reason (1794)

I believe in one God, and no more; and I hope for happiness beyond this life.

I believe in the equality of man, and I believe that religious duties consist in doing justice, loving mercy, and endeavoring to make our fellow creatures happy.

But lest it should be supposed that I believe many other things in addition to these, I shall, in the progress of this work, declare the things I do not believe and my reasons for not believing them.

I do not believe in the creed professed by the Jewish church, by the Roman church, by the Greek church, by the Turkish church, by the Protestant church, nor by any church that I know of. My own mind is my own church.

All national institutions of churches—whether Jewish, Christian, or Turkish—appear to me no other than human inventions set up to terrify and enslave mankind and monopolize power and profit.

I do not mean by this declaration to condemn those who believe otherwise. They have the same right to their belief as I have to mine. But it is necessary to the happiness of man that he be mentally faithful to himself. Infidelity does not consist in believing or in disbelieving; it consists in professing to believe what he does not believe.

It is impossible to calculate the moral mischief, if I may so express it, that mental lying has produced in society. When a man has so far corrupted and prostituted the chastity of his mind as to subscribe his professional belief to things he does not believe, he has prepared himself for the commission of every other crime. He takes up the trade of a priest for the sake of gain, and, in order to qualify himself for that trade, he begins with a perjury. Can we conceive anything more destructive to morality than this?

Source: http://www.wsu.edu/~wldciv/world_civ_reader/world_civ_reader_2/paine.html