WHAT IS THE ORIGIN OF HOT-CROSS BUNS? The custom of making bread marked with the sign of a cross for consumption at festivals is both ancient and widespread. There is no ground for supposing that the custom originated with the early Christians; they merely altered its significance by associating it with the Sacrament of the Lord's Supper.
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.