Nathaniel Hawthorne's Scarlet Letter is one of those books you hear about from time to time. I'd never read it but I eventually got round to it the other week. The lead in is a little long winded but Hawthorne wants to root you in his present before taking you back to yesteryear and a very different New England. I had always assumed that scarlet letter referred to a letter written in red ink, which is not the case. It is a little anti-puritan but I enjoyed the book as it is well written, the story well told and very human and with a little whiff of the mysterious, which is both true to life and makes for interesting reading. I'm glad to have it read (no pun there).
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.