He was wounded for our transgressions, he was bruised for our iniquities (Is 53:5). It should be carefully noted that the sign given of the Saviour’s birth is not a child enfolded in Tyrian purple, but one wrapped round with rough pieces of cloth: he is not to be found in an ornate golden bed, but in a manger. The meaning of this is that he did not merely take upon himself our lowly mortality, but for our sakes took upon himself the clothing of the poor. Though he was rich, yet for our sake he became poor, so that by his poverty we might become rich (cf. 2 Cor 8:9); though he was Lord of heaven, he became a poor man on earth, to teach those who lived on earth that by poverty of spirit they might win the kingdom of heaven.
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.