I did not understand ......

As a counterpoint to existing comments about this book, I confess I do not understand the intent of the author.
Here we are in the presence of a fifties who veto the beginning of the novel confesses his disenchantment with life (he is in full mourning his grandmother), he is a widower, and he slays "an average of two dogs per week on Wednesday ".
And the Virgin appeared to him first of April. For me it was the right idea. What is he doing? Well visit to the doctor, the psychiatrist and the priest, bishop and finally Lourdes. In passing he made a pair of unlikely friendships with believers, others would say the clam frogs, slipping it into the pocket their private requests, since it is related to the Virgin. Mariette emerges lot more human than the others no doubt.
In passing, he discovered that in fact the woman could now fill the emotional void in his life is his assistant Rose Marie (another pun?) After a lewd sex scene in his office by the so-called Louise which will only a brief passage in the novel.
Pierre will be three apparitions of the Virgin, all silent except a cryptic phrase in the Lourdes Grotto, but the second it will launch a stone (pun?).
Back in Paris, and after Lourdes, comes the death of Mariette, her favorite bigoted, stopping his psychotherapy which cost him dearly, and the beginning of a new life with Rose Marie.
The tone is humorous, sometimes he succeeds.
Anyway I did not understand this novel nor its plot or its purpose. Too bad because the theme of an apparition of the Virgin first of April, I think there was a great literary edifice to build rather than very light novel.