I read this little book on the history of capital punishment in Britain the other week. Judicial hanging is its main theme but it touches on burning, beheading, etc. It talks about forgotten matters such as the Halifax Gibbet and boiling people to death amongst other things. It covers some of the most gruesome passages of British history but not in a sensationalist way. The main story is of the development of better hanging techniques and of the hangmen who were sometimes drunks. I am in favour of capital punishment to some extent but this book shows how very difficult it is to come up with a method of execution that is anywhere near humane.
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.