My youngest son was 12 yesterday. His best (and cheapest) present was a bag of army men. He (and I) really enjoyed playing with them after tea. We shared them out and then had a battle using two dice and rules that we made up as we went on. He won. Great stuff. Later we played consequences and categories in the front room.
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.