I've been thinking about the Christmas of 1964 and I think it must have been that Christmas that I also received an orange plastic Beatles guitar as above. The guitar survived for many years without strings serving as a prop for miming to records. I had forgotten it had only four strings. Not an issue at the 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.