Initial reviews of Mere Christianity generally show enthusiasm,[5] and most of them were from Christian publications.[6] However, combining them with the reviews published decades later indicated a more mixed reception.[7] The historian Stephanie L. Derrick observed that the book's literary elements, such as its eloquence, were the aspect most frequently noted by contemporary publications.[5] The historian George M. Marsden summarised that Mere Christianity "has been hated as well as loved. Nonetheless, as a popular presentation of the faith it has drawn less systematic criticism than would a book that purported to be a definitive treatise on Christian apologetics and theology."[8] On the general reception to the book, the Lewis biographer Margaret Patterson Hannay described it as his "most popular and ... most disparaged" work, adding that "probably because its fans have spoken of it as a profound piece of theology, while it is, as was designed to be, only a primer".[9]
Describing the book as "a rare gift", Edward Skillin of the Commonweal magazine commented of Lewis's ability to make "complicated matters" more accessible especially to laypeople.[5] On a passage of the book, Edward D. Myers of Theology Today noted, "This is clear, it is simple, it is eminently Christian, and it is typical of the ease with which Mr. Lewis puts great matters into plain language."[5] Joseph McSorley of The Catholic World found Lewis writing "with his customary clarity and incisiveness, and with proofs that the average man will find convincing. It is a delight to see him demolish in a paragraph many of the heresies which have contributed to our present ghastly condition."[10] The Tablet, a Catholic magazine, wrote:
"We have never read arguments better marshalled and handled so that they can be remembered, or any book more useful to the Christian, in the Army or elsewhere, who finds himself called upon to argue briefly from first premises, to say why morality is not herd-instinct, why there is a special and unique character attaching to the sense of obligation, why the conviction that there is a law of right and wrong and a transcendent morality is only intelligible if there is a God."[11]
The Times Literary Supplement wrote of Lewis's "quite unique power" of making theology interesting, even "exciting and (one might almost say) uproariously funny".[7] The reviewer added: "No writer of popular apologetics today is more effective than Mr. C. S. Lewis."[12] The Clergy Review's G. D. Smith opined that Lewis "shows himself a master in the rare art of conveying profound truths in simple and compelling language".[12] J. H. Homes of the New York Herald Tribune Weekly Book Review wrote that "his clarity of thought and simplicity of expression have a magic about them which makes plain the most abstruse problems of theological speculation".[7] The Guardian said: "His learning is abundantly seasoned with common sense, his humor and his irony are always at the service of the most serious purposes, and his originality is the offspring of enthusiastically loyal orthodoxy."[12]
"Mere Christianity is a popular, not an academic, book, which is not directed towards a readership of academic theologians or philosophers. It is simply unfair to expect Lewis to engage here with detailed philosophical debates, when these would clearly turn his brisk, highly readable book into a quagmire of fine philosophical distinctions. Mere Christianity is an informal handshake to begin a more formal acquaintance and conversation."
—Alister McGrath on the book's readability[13]
The author Colin Duriez praised it as easy to understand,[14] and the biographer Thomas C. Peters opined that his straightforward language makes the book fit to a wide audience.[15] There had been also criticism, which was primarily directed towards Lewis's "Liar, lunatic, or Lord" trilemma.[16] The Lewis biographer and Christian apologist Alister McGrath, while commending the book in general, felt that his trilemma is a weak defence for the doctrine of the divinity of Jesus, calling this the book's "most obvious concern".[17] He wrote his argument is mostly unsupported by the modern biblical scholarship, and argued that others options such as that Jesus was mistaken about his identity should have gotten into consideration of alternatives.[18]
Scathing criticism came from the philosopher John Beversluis, in his book C. S. Lewis and the Search for Rational Religion (1985).[8] Beversluis analysed Lewis's arguments for Christianity, arriving in the conclusion that each of them is built on faulty logic.[19] He argued that Lewis made his arguments convincing by creating false analogies, with an instance in his trilemma.[20] Beversluis said there are more alternatives in addition to Jesus being a liar or lunatic, one of which is that his disciples misinterpreted his words.[20] The philosopher Victor Reppert replied to Beversluis in C. S. Lewis's Dangerous Idea (2003), noting that Beversluis was correct in pointing out that many of Lewis's arguments are not strictly logical but overestimating the degree to which Lewis rested his case for Christianity on reason alone.[21] Reppert continued that Lewis, in his autobiography, Surprised by Joy (1955), realised Christianity rests on far more than solely reason.[22]
