Henri Daniel-Rops described his career thus:
Perhaps this is a good time to explain how it happened that while I was an essayist and novelist up to 1939, I then found myself orientated in an entirely new direction, that of religious history. Here again, it was a providential introduction to someone that changed the course of my writing career. In January of 1941, a friend of mine, the historian Octave Aubry, asked me if I would care to write a volume of history for a series he was editing. From the outset I was very interested, but I was uncertain what subject I should choose. This was at the time when the Nazis had forced the Jews to wear the yellow star to distinguish them from the other races. That had made me very angry, especially when I thought of all the Jews who were my friends. And so my answer to Octave Aubry was: "I accept, on condition that I may write a history of Israel." He immediately agreed to my choice of subject.
I must say here that I had long regretted the fact that in our schools we study the Greek and Roman classics but neglect the important if not basic classic of our western civilization, the Bible. At last I was offered the opportunity of making an extensive study of it. And so I wrote l'Histoire Saints (Sacred History). It was published in Paris on July 1, 1943, just twenty days before the Nazis arrived, when it was immediately confiscated by the Gestapo and the plates destroyed, without doubt because Hitler recognized himself in Nabuchodonosor!
From that time on, this historical series became my constant preoccupation. Begun on January 19, 1941--on my fortieth birthday--this series is still in progress and, God willing, it will continue for at least five more years. If anyone had mentioned to me in the beginning that I would write seven thousand pages, there is no doubt in my mind that I would have hesitated to undertake such a task. But, as I said, it was Providence that prompted me; one is guided thus.
Preoccupation, did I say . . . . After l'Histoire Sainte came Jesus et Son Temps, the success of which greatly Surprised me: actually in France alone 400,000 copies have been sold mid the work has been translated into fourteen languages.
Having written of Jesus, was it possible not to be moved to write of the work born of the Son of God and which is His visible sign upon earth, the Church? And so L'Histoire de I'Eglise du Christ came slowly into being. Without being too egotistical, may I say that the response which I have received for this work has been most encouraging for me in the long and arduous writing of the series. I would like at this time to especially acknowledge the kindness of the late Pope Pius XII who often asked me about my writing and who was most generous in counseling me, and also His Holiness Pope John XXIII who likewise conferred a papal honor upon me.
Let me repeat that I am enthused with my work as well as completely immersed in it. In my future there was to be a little book, Missa Est. Under the title of This is the Mass, thanks to the promotion of my American publisher, Hawthorn Books, and the kindly cooperation of the Most Reverend Bishop Fulton Sheen, it has also been very well received.
And there was to come the founding of my monthly review, Ecclesia [similar to The Catholic Digest] in 1949 and so now is more than twelve years old. There was to come, too, L 'Encyclopedie du Catholique au XXeme siècle (The Twentieth Century Encyclopedia of Catholicism), "Je sais, Je crois." For me to conceive, to organize and to launch this last work fulfilled one of my highest ambitions.
And so you see the apple tree continues to produce its apples. Of what value are these apples it is not for the tree to say. But how can one do other, dear God, than try to produce good fruit, keeping in mind the fig tree of the Gospels which, when it was found to be barren, was fit only to be cast into the fire?
But I have already spoken too long about myself. Nevertheless this backward glance, which I have been asked to make, has enabled me to take stock of what I have tried to do. And I feel that my work will not have been in vain if the reader, after pouring over so many pages, will find in them just one sentence which will influence him for eternity, one sentence which will move him to forgive and forget all that is worthless in them and so destined to disappear some day one sentence which will send him back to the words of the Evangelist who summed it all up: 'To whom shall we go, Lord? You alone have the words of eternal life."
More about Daniel-Rops and his popularity in mid-twentieth century Catholic France here. In the USA, his series on Church history was published by Dent Dutton in hardcover and then by Doubleday Image in paperback.