What is the origin of mind your P's and Q's? Various theories have been put forward. Some say that it was a warning to printers apprentices when sorting type, the letters p and q being almost identical in form, others that it was used in inns, the amount owing being chalked on a board in order that customers should not order more than they could pay for when settling day arrived.
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.