At the time this novel was published, it was generally regarded as Cronin’s greatest work. Published by the Book-of-the-Month Club, the novel received an enormous readership and was greatly acclaimed by an overwhelming majority of the critics, although there were some negative comments about the sentimental and often melodramatic elements that feature much of the plot.
Yet, though literary critics, for the most part, commented favorably, there was greater division on the part of critics found in religious publications. These critics found little evidence of orthodox Christianity in the novel and were dissatisfied with the kind of religious example offered by Cronin in the life of his protagonist. Catholic literary critics were also divided in their views of the work, many of them believing that Cronin had distorted the goals and motivations of the priesthood and that he had not drawn a sympathetic portrayal of the Catholic Church on the whole.
This claim is perhaps true, for it does seem that Cronin has drawn not so much a model for one faith but a model for all faiths, and this may be why this novel remains the most widely read of all of Cronin’s offerings. Medical doctors, too, complained bitterly about Cronin’s The Citadel (1937), one of his major novels dealing with some of the evils practiced by medical men. Because Cronin was a medical doctor himself, however, there was a general acceptance of his views on how medicine was being practiced. As he was never a priest, some of Cronin’s critics, especially those writing for religious publications, believed that he had not been entirely fair to organized religion.
Nevertheless, The Keys of the Kingdom, because it depicts an inspiring journey in the spiritual life of a saintly man, continues to be enjoyed by many readers and is still regarded as Cronin’s greatest novel.