“Speaking as of today, I do not consider it intellectually respectable to be a partisan in matters of religion. I see religion as I see such other basic fascinations as art and science, in which there is room for many different approaches, styles, techniques, and opinions. Thus I am not formally a committed member of any creed or sect and hold no particular religious view or doctrine as absolute. I deplore missionary zeal, and consider excessive dedication to and advocacy of any particular religion, as either the best or the only true way, an almost irreligious arrogance. Yet my work and my life are fully concerned with religion, and the mystery of being is my supreme fascination, though, as a shameless mystic, I am more interested in religion as feeling and experience than as conception and theory.”

1920s, Truth is a Pathless Land (1929)
Context: I maintain that Truth is a pathless land, and you cannot approach it by any path whatsoever, by any religion, by any sect. That is my point of view, and I adhere to that absolutely and unconditionally. Truth, being limitless, unconditioned, unapproachable by any path whatsoever, cannot be organized; nor should any organization be formed to lead or to coerce people along any particular path. If you first understand that, then you will see how impossible it is to organize a belief. A belief is purely an individual matter, and you cannot and must not organize it. If you do, it becomes dead, crystallized; it becomes a creed, a sect, a religion, to be imposed on others. This is what everyone throughout the world is attempting to do. Truth is narrowed down and made a plaything for those who are weak, for those who are only momentarily discontented. Truth cannot be brought down, rather the individual must make the effort to ascend to it. You cannot bring the mountain-top to the valley. If you would attain to the mountain-top you must pass through the valley, climb the steeps, unafraid of the dangerous precipices.

Occulture: Secular Spirituality, pp. 111-112
The Ahuman Manifesto: Activism for the End of the Anthropocene (2020)

1960, Speech to the Greater Houston Ministerial Association
Context: But let me say, with respect to other countries, that I am wholly opposed to the state being used by any religious group, Catholic or Protestant, to compel, prohibit, or persecute the free exercise of any other religion. And I hope that you and I condemn with equal fervor those nations which deny their Presidency to Protestants and those which deny it to Catholics.

As quoted in The Life and Writings of Thomas Jefferson : Including All of His Important Utterances on Public Questions (1900) by Samuel E. Forman, p. 429
Posthumous publications

Responding to http://lists.wikimedia.org/pipermail/wikien-l/2007-March/066648.html the deletion of a Wikipedia article from non-administrator view, while the article's deletion was being reviewed by the community. (27 March 2007)

Parade (1 February 1981); cited in Thy Kingdom Come : How the Religious Right Distorts Faith and Threatens America (2007)

Election address for the 1885 general election, quoted in Blanche E. C. Dugdale, Arthur James Balfour, First Earl of Balfour, K.G., O.M., F.R.S., Etc. 1848–1905 (London: Hutchinson & Co. Ltd, 1936), p. 72
President of the Local Government Board

Speech delivered at Freemasons’ Hall, Great Queen Street, London, in a meeting held to constitute a Theistic Association in London on 20th July 1870. See Universal Religion for full speech.

Source: On the Origin of Species (1859), chapter XV: "Recapitulation and Conclusion", page 421 http://darwin-online.org.uk/content/frameset?pageseq=449&itemID=F391&viewtype=image, in the sixth (1872) edition
Source: The Origin of Species