Today, at church, the priest was discussing the Sacrament of Reconciliation, both commenting on how even priests and nuns go to Confession regularly and on how, as a priest, he's noticed that people tend to come in with the same sins week after week, so he sometimes wondered how many of us truly examine ourselves and try to improve yourselves (this being in light of the Gospel reading about the three servants entrusted with their master's wealth, and what they did with them).
I think I read this in the mid 1990s. I remember the author had several books, all in a dark humor category, but I can't recall his name, although I remember the concept of religious orders popping up in another series. This book was a standalone. The main character was an adult male who is a member of a religious (Catholic, I'm pretty sure) order that sequestered themselves away from the world in order to pursue a life of quiet contemplation and prayer. As I recall it, he was trying to be a good member of the order, but didn't quite feel like he reached the right level of piety despite his attempts. I recall that he commented on how they were expected to go to Confession regularly, and were not allowed to leave without confessing something, which led to him making up sins, and then feeling guilty about lying, and confessing those lies. What kicked off the plot was that something is going on with the order where they needed to send someone out into the world to resolve a matter, I think maybe involving some aspect of land ownership where the monastery is? The protagonist is chosen to go into the outside world, which is set somewhere in the 1970s to 1990s, I think (nothing stuck out as being particularly "old" sounding, but I don't remember cell phones coming up, or the Internet).
After that, I don't remember much of the rest of the plot. It's largely humor about the protagonist being a fish out of water, dealing with the sinful regular world, and when he returns to the monastery (I think successful in his endeavor), he at first thinks the outside world has corrupted him, but he instead realizes that he joined the monastery not out of devotion, but as a way to escape his former life, and that that is the wrong motivation. I do remember that he takes a trip on an airplane and experiences the wonders of miniature liquor bottles (I want to say they were complimentary, which would probably date this story as being further in the past when there wasn't as much cost-cutting and flying was seen as a luxury experience), and I think he comes home with a suitcase full of them, many of them empty because he just likes the way they clink together.
It was a hardback, probably in the 200-300 page range, and when I read it, it looked at least a few years old. The pages had some wear and were starting to darken with age, but didn't seem yellow and brittle.