The microphone is a limiting, and rather irritating, instrument, but the quality of thinking and depth of conviction which I find in your book ought sure to be shared with a great many other people.

[1] In the preface to later editions, Lewis described his desire to avoid contested theological doctrine by focusing on core beliefs of the Christian Faith.

The timing of these talks was important and strictly adhered to due to technology and World War II, Germany would broadcast propaganda through the English-spoken "Lord Hawhaw" during any dead air.

After introducing the moral law, Lewis argues that thirst reflects the fact that people naturally need water, and there is no other substance which satisfies that need.

Lewis also covers such topics as social relations and forgiveness, sexual ethics and the tenets of Christian marriage, and the relationship between morality and psychoanalysis.

[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.

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.

"[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".

"[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.

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.

[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.

[31] Analysing Lewis's books, the Australian archeologist Warwick Ball believed Mere Christianity is perhaps his most influential and widely read apologetic work;[32] the American philosopher C. Stephen Evans called his moral argument the "most widely-convincing apologetic argument of the twentieth century";[33] McGrath considered it "perhaps as outstanding an example of a lucid and intelligent presentation of the rational and moral case for Christian belief as we are ever likely to see".

"[38] According to the authors Roger Lancelyn Green and Walter Hooper, its success led to the acknowledgment of Lewis as "one of the most 'original' exponents of the Christian faith" of the 20th century.

[42] The author Marvin D. Hinten wrote: "When people are asked which C. S. Lewis book has most influenced them spiritually, the most common answer is Mere Christianity.

[51] For instance, soon after the dissolution of the Soviet Union, it was translated into the several native languages of its breakaway states, which was done by Orthodox Christians to rebuild their influence.

[55][56] The American attorney Charles Colson's conversion happened after him reading a copy of the book given by his friend, Thomas L. Phillips (the chairman of the board of the Raytheon Company).

[69][70] Paul McCusker's C. S. Lewis & Mere Christianity, which provides insights to the work in its historical context, was published in 2014; it was praised for being well-researched but was criticised for its factual errors.