I first discovered the series of albums that became the Introspection series as a teenager. There are five altogether (1-4 plus '92 the homage album to Rogier Van Otterloo one of the major forces behind these albums). Number 2 is my favourite but the others are fine too. The 1975 album uses an orchestra with Thijs Van Leer's flute plus the voice of Letty de Jong, an electric bass, Spanish guitar, snare drums and piano at times and creates a very attractive soundscape that I suppose would be called light classical. Some tracks are rearranged classical pieces (Granados, Cimarosa, Handel and Bach) while other pieces are modern ones by Van Leer (including Focus III) and Van Otterloo (Rondo and Introspection). Part of the pleasure is in knowing that this very sedate album features the man who also plays on Hocus Pocus but it is just a very good album anyway in a relaxing sort of way.
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.