I read your blog occassionally, though this is the first time I comment. It was through your post on Sertillanges that I first found your blog. I enjoy your writings.
Good observations about Agatha Christie.
I'm a Catholic, too.
I too had noticed that she made some of her significant characters (e.g., Amy Carnaby in The Flock of Geryon) treat the Catholic Church with a bit of disdain. But then I was surprised to read in The Adventure of the Christmas Pudding that when Col. Lacey says that midnight Mass is too much like "Popery" he then apologises to Hercule Poirot.
After that my curiosity was aroused and I tried to find out if Agatha Christie had ever mentioned Poirot's religion explicitly somewhere. Later, while reading The Apples of Hesperides in The Labours of Hercules, I was pleasantly surprised to learn that Poirot was "a Catholic by birth."
Later, I was even more surprised and happy to read in the short story The Chocolate Box Hercule Poirot saying to Capt. Hastings, "I am, as you also know, bon catholique ...."
I don't know Agatha Christie's opinion of Catholicism in general, (I have recently bought her autobiography. Perhaps, after reading that, I might learn what she thought about Catholicism.)
However, I do know that she signed a petition to Pope Paul VI requesting permission for the use of the Tridentine Mass in England and Wales. You can read about it here:
It's great to read those parts in the novels and short stories when Poirot upholds the good of the family, marriage, and appeals passionately to the plans and the will of Le bon Dieu.
I found one half of your third point different from my experience, since there have been times when I didn't particularly enjoy the plot-line of some novel or short-story, but I read it anyway simply because Poirot was in it. I, personally, would very much love to meet Hercule Poirot in person. (Though he would probably have a heart attack if he saw my room - complete lack of any order and method.) As a character, he is fascinating and unique.
Mrs. Marple, however, I don't find appealing as a character.
With love and prayers,
Yours in Christ,
I'm not as well read in Christie as this reader. I'm glad to see that through Poirot she gives Catholicism its due.