Why do we shake hands on meeting? Students of folk-lore trace the origin of handshaking to primitive magic; the physical contact of the hands symbolised that each of the parties yielded himself up to the power of the other and united with him in peace and friendship; or signified the ratification of a compact or pledge. We still clinch an agreement or a business deal by “shaking hands on it.” This element of contact is clearly seen in the Roman marriage ceremony, in which – as also among the ancient Hindus – the clasping of hands by the bridge and bridegroom was a prominent feature.
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.