Having read one of Iain Pears' novels recently I popped along to my local library to see what they had and took out a paperback of The Portrait which was okay, though Mr Pears doesn't make it easy for himself by giving the whole narrative in the first person soliloquy of an artist as he paints a portrait of an art critic. There's a nice twist towards the end although when you think about an artist painting a critic there can only be one likely ending. By the way I should urge caution on anyone deciding to read it. My main difficulty I guess with reading it was not knowing enough about art. When Mr Pears mixes fact and fiction I'm not sure which is which. Anyway he hasn't put me off and I'll probably read another of his novels some time.
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.