For those who believe no proof is necessary

I was looking for the originator of this quote and found it both surprisingly difficult and incredibly easy to locate: the easy part is that quoteinvestigator.com has an excellent article detailing its appearance over the years; and the difficult part is that it doesn't show up in search results unless you know exactly what to search for (hence why I'm posting it here).

First off, to cut to the chase, QI concludes that its first known appearance was in an editorial in the St. Louis Post-Dispatch from December 1882, author unknown (there, its form is: "No explanation is needed for a believer; no explanation suffices for an unbeliever.")

From my searches, however, it seems that it has most often been attributed to Franz Werfel, Joseph Dunninger, Thomas Aquinas and Stuart Chase.

For Aquinas, it is rendered "To one who has faith, no explanation is necessary. To one without faith, no explanation is possible". This version features among the top search results for "Aquinas quotes", and one Christian writer calls it "probably the most popular St. Thomas Aquinas quote on faith".

It does not, however, feature in the writings of Aquinas - though similar sentiments appear in this passage, from S.T. II-II, Q. 1, Art. 5, reply obj. 1:

“Unbelievers are in ignorance of things that are of faith, for neither do they see or know them in themselves, nor do they know them to be credible. The faithful, on the other hand, know them, not as by demonstration, but by the light of faith which makes them see that they ought to believe them, as stated above”

https://books.google.com/books?id=MVZODwAAQBAJ&pg=PT2135

Werfel and Dunninger (among others) are explained in the QI article. Werfel's connection comes one step removed from the 1943 film adaption of his 1941 novel "The Song of Bernadette", where the words "For those who believe in God no explanation is necessary. For those who do not believe in God no explanation is possible" appear during the prologue. The sentiment is not present in the English version of the novel - nor presumably the German version - and this particular iteration appears to be taken from the words of Father John LaFarge, a Catholic priest, after an article in Fortune written around 1934 (though it was later credited to the screenwriter of the film, George Seaton, in the 1997 Chambers Dictionary of Quotations).

Dunninger was a skeptic, debunker, and something of a prototype for James Randi, so presumably used the quote in an ironic way (his version: “For those who believe, no explanation is necessary. For those who do not believe, no explanation is possible.”)

As for Stuart Chase, who seems to be the most popular current 'source' for the quote - according to Brainquotes, Goodreads, AZQuote, all those "excellent" quote mill places - I don't see how it came to be attached to him. Using Google's time tool (assuming it's accurate), it looks like it popped up on AZQuotes some time in 2004 and then slowly began to appear on more sites each year. There is a 2011 International Skeptics thread that speculates it may have come from his 1925 book 'The Tragedy of Waste', but I've searched the book online - presumably it wasn't available to them at the time - and nothing resembling the quote appears there.

In a nutshell, it wasn't Chase, it was some unknown (presumably) Missourian living in the 1880s - though Thomas Aquinas wrote something along the same lines quite a few years before.

And hopefully now it's easier for Google to assist others in finding that out.