As Garwood explains in her unique book about Flat Earth belief; no Christian believed in a flat earth. The only exceptions were the minor Christian writers Lactantius and Cosmo [4th and 6th centuries, and both were quite insane]. Educated people today know this.
Interestingly however, in the heyday of Darwin, naturalism and pond scum to people theologizing we do see a revival – as outlined by Garwood – of the flat-earth concept. The age of 'reason' it appears was not entirely reasonable. It makes for interesting reading. The progenitor of this debauched idea was a man named Parallax, a successful doctor with many names, who became wealthy from quackery. Like many in the 2nd half of the 19th century, Parallax, a very smart, urbane man, enriched himself by selling nonsense and snake oil. A variety of condiments created by Parallax supposedly cured everything from old age to ugliness. He would do very well today selling to modern vanity.
For some reason, though only a nominal Christian, Parallax decided to fight the burgeoning institutions of 'science' through advocating a 'flat earth'. Why? The silos of scientific thought and endeavour were rapidly forming post 1860. Today we reap the results of this 'professionalization'. 'Experts' with advanced degrees in trivia dominate the journals and academia. Pathetic theories with no basis in science or applicable methods caper everywhere. By 1870 such trends were in blossom. Science was corrupted in the 19th century, as it is today, by special interests, cabals, unscientific processes, egos and lies.
Parallax was active in writing, debating and through the use of psuedo-science and rhetoric, 'smashing' the lies that the earth was a sphere. He set up fraudulent experiments, made his opponents look silly in debates and issued a flood of rhetoric and scientific sounding gibberish to back up his theory that the earth was flat. Many people were convinced. He also openly appealed to the Bible. By so doing he invited the critics to associate Christianity with Flat Earth beliefs. Reading his story in Garwood's book is recommended. It should also be emphasized that Parallax never believed in a flat earth. He did it for fun and to make money. A very smart, yet somewhat jaded and impish man.
Sadly, some of his acolytes who were devoted Christians took up Parallax's Flat Earth campaign. John Hampden [during 1870-1885] and Lady Blount [ca 1880-1910] were the most infamous. The Flat Earthers named themselves 'Zetetics' and advertised themselves as truth-seekers. Both Hampden and Blount were Bible literalists who tortured the translation of the Bible and certain Hebrew words to support their Flat Earth ideals. Both were mentally unstable and quite ignorant.
“Lady Blount’s views about the shape of the earth were almost identical to those propounded by Parallax and Hampden, although she placed an even heavier emphasis on the Biblical basis of her ideas. With a Leicester associate, Albert Smith, otherwise known as ‘Zetetes’, she produced a simple summary of this scriptural world view: Heaven is above the earth (not all round), earth beneath, and water under the earth (Exodus 20:1-4).....”
She used many other verses incorrectly. For example Exodus 20:1-4 does not say that the earth is flat.
20:4 “You shall not make for yourself an image in the form of anything in heaven above or on the earth beneath or in the waters below.”
Waters below the earth does not mean that the waters are somehow on the other side of the earth. This verse means that humans should not make idols from any form of life found in water. That is all it means.
Blount and other literalists misused scripture to put forward unscientific ideas, long rejected by Christians dating from the time of Christ. Sadly they have provided a tenuous link for cults to wrongly associate Christian theology with naturalist science and the idea of a flat-earth [much defended as an idea pre-Aristarchus in ancient Greece as well]. For example we have:
“He sits enthroned above the circle of the earth...” Isaiah 40:22
“He will assemble the scattered people of Judah from the four quarters of the earth.” Isaiah 11:12
There are incorrect translations of Isaiah 40:22 using the word sphere in place of circle. The original Hebrew word chuwg likely refers to a circle, of 3 dimensions or perhaps even 1 dimension. No one really knows. In any event in this passage by Isaiah [as with most of the Old Testament prophets], the context is obviously poetic. The Bible is not a science document. The Old Testament is about prophecies, histories, wars and commandments. If you read the entirety of the passage from Isaiah you will find that people are described as grasshoppers.
In the 2nd verse given above, some translations will insert corners for quarters. This is also not a literal reference to the shape of the earth. Even today we sometimes use the expression the four corners of the earth and what we mean of course, are the 4 directions on a compass. The same was true of the ancients. They were not stupid as many today assume.
The point is that cranks such as Hampden and Blount were not even good Christians. They perverted translations of words from Hebrew and Greek to justify their cultish obsessions around a flat earth ideal. As with other cult doctrines, fabrication, corruption and mendacity do not inform science or reason. It is a pity that such literalists misuse Biblical text to market their absurdity.