I came across a young man wearing this t-shirt today. I saw it from the back first. It's difficult not to say something. He wasn't sure what a sinner was. His girl friend thought it was a criminal. I explained that we are all sinners and need God's grace. I should have gone further.
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.