It's a fear of death, in particular nasty, brutish forms of death. That's why I associated the development of the diabolical with the events of the day, the fall of the Roman Empire and arrival of barbarian dark ages (for all that the study of the period has proved they were not as dark as was considered in my youth), the plagues of the end of the 14th century, the Wars of Religion and the plagues which followed, and the aftermath of the Industrial Revolution, with the ravages of disease seen in the late Victorian - the PR understates just how bad the death count of the 1850s actually was.

Each time, some cultural parasite (the Church, neopaganism) hooks into it. Let's not fall victim to it again, if ebola gets out of control.

For all I can see, the earliest use of the veil imagery in this sense goes back to Harriet Beecher Stowe in the mid 19th Century. She hooked into other forms of mysticism, in the Veronica veil, retained as a cult relic of the Crucifixion in one of Poussin's four iconastases of the St Peter's Baldaccino in the Vatican, and possibly the Milan shroud. This sense often occurs in the momento mori tomb effigies of the fourteenth century, showing the life form above and the shrouded skeleton underneath. That in turn moves into the shrouded form of "Fatso" ghost. However, that is a veil between the life form and the death form, not the spiritual form. The general sense in the Roman creed is studied here, which has nothing to do with the subject at hand: it serves to cover the angles one might look for in Aquinas and Augustine, however, in support of my hypothesis that the real roots lie in pseudo-Arthurian feminist texts typified by the work of Marion Zimmer Bradley, taking the work of the Victorian neogothicists on to the heart of the neowiccan and pagan imagery indicated.