In the New York Times review of this novel, it is written that
Fuentes has written--in addition to a good novel and a gripping narrative--a thinly-disguised but most compelling Catholic tract.
With regard to the question of the relationship of the Catholic Church and the elite, as far back as the medieval age it was the elite who often entered the clergy. For instance, in France the Norman custom of the firstborn inheriting the estate was in place, leaving the other sons with little. Since the Catholic Church wielded both spiritual and political power as the Second Estate, many of the sons who were not first-born entered the clergy because they could wield influence in the same realm in which they had grown up. They certainly related well to the aristocrats whose money built the cathedrals and supported the clergy. After all, many of their families knew each other well.
In Mexico, while the clergy are not often from the upper classes, they are certainly well acquainted with families of wealth as these have been the people who have supported the churches. In fact, long-time restrictions by the government upon the churches has made them dependent upon the contributions of the wealthy. (Unfortunately, some of the "wealthy" are among the criminal element in contemporary times.)
Often, too, priests are practically personal counselors and advisers for their wealthier parishioners. Certainly, religion is a major part of the culture, and the Catholic Church has strict rules and often great guilt is placed upon people who transgress.