What is the origin of nicknames? Primitive man's habit of regarding his real name as his own private property and so rarely if ever to be used. To his companions he was therefore known by what was formerly called in England an eke (ie added) name. Slovenly pronunciation turned this into a nickname.
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.