I have now listened to all 35 lectures from Dr David Calhoun on ancient and medieval church history given I the nineties at Covenant Theological Seminary. Each lecture is around 45 minutes in length and is a helpful introduction or refresher course in the main points of the history of the period from a Christian point of view. Church history is the subject rather than theology as such but there is some helpful stuff here all delivered in a warm and helpful way and well worth checking out. They are available on itunes u.
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.