It left me wondering exactly when it was that Christianity, its imagery, its doctrines, lost their grip on the human imagination.
I think there's a definite watershed. You can narrow it down by looking at religious art and literature. On one side the figure of Jesus (say) is still relete with spiritual authority, on the other he's just a kindly young man in a nightie.
In English culture this divide comes somewhere towards the end of the 17th century- with the dying out of the generation that fought the Civil War- which was in part a religious war. On the one side of the divide you have the Puritan absolutism of the Pilgrim's Progress and the confident assertion of Henry Vaughan's
My soul there is a country
Far beyond the stars
Where stands a winged sentry
All skillful in the wars...
And on the other... well, I'm pushed to find examples because all the religious art is so forgettable. Dutiful, plodding, unconvincing. It's not that people didn't believe- obviously they did at some level of their beings- but religious sincerity is hard to fake- especially in art- and it just can't be found any more. The old stories and images no longer inspire. The 18th century is void of first rate religious art- with the exception of a few odd things by "madmen" like Christopher Smart and William Blake. If pushed one might allow "amazing Grace"- a lyric by John Newton "the old African blasphemer" a man of the same stamp as Bunyan- coarse, proletrarian, unyielding- but not the hymns of Charles Wesley- which are drily theological and only made bearable by their tunes.
With the 19th century things get worse. The Victorians have realised they don't really believe any more and it panics them and they take to beating the old images to make them get up - and only succeed in raising dust. Glittery dust. Victorian religious art is terrible- sentimental, simperingly false, hysterical...
In Italy the crisis came earlier. You can observe it in time as it washes over Michelangelo- perhaps the last great medieval Catholic artist- inflating his figures, blowing them up like Michelin men, as if doubt could be silenced by the flexing of muscles. The Last Judgement in the Sistine Chapel is a monstrous piece of grotesquerie- a convocation of body builders with Jesus as the biggest muscle Mary of them all.