As we were going to be in Edinburgh, I decided to try the first Rebus novel by Ian Rankin Knots and crosses. The Edinburgh setting is not crucial but there was some pleasure in picking up on the few geographical references. The book is deservedly considered a decent one. No doubt a knowledge of the whole series would add to the pleasure. Like most such novels it deal with some fairly sordid details. Perhaps the most interesting element is the idea that Rebus is some sort of backslidden Christian. It would be interesting to see how that plays out in other novels.
Bonhoeffer uses a similar phrase 'worldly Christianity'. It's J Gresham Machen that I want to line up most closely with. See his Christianity and culture here. Having done commentaries on Proverbs (Heavenly Wisdom) and Song of Songs (Heavenly Love), a matching title for Ecclesiastes would be Heavenly Worldliness. For my stance on worldliness, see 3 posts here.