I should have mentioned that Rhodri and I enjoyed a nice free exhibiition at the British Library last Monday. (Tip off from Principal S - thanks!). Called Evolving English it is a very well done cruise through the history and development of the language in conjunction with a book by good old David Crystal. See the website here. Have a go at the quiz. Rhodri and I drew 5 all.
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.