Franklin’s cathedral

This is something I found on Tumblr. The artist is Franklin Booth, apparently he specialised in absurdly detailed drawings of this sort (you can click on it to enlarge) because he saw the illustrations in magazines from when he was young and didn’t realise they were actually made from wood engravings, so he set out to recreate that sort of detail and texture with pen and ink.

From what I can find, this is an illustration for a story called “A Remembered Dream” written by one Henry van Dyke and published in 1917 in Scribner’s. I have not read this story, no idea what it’s about (apart from what the title perhaps indicates), and I’m just mesmerised by this image from it. What’s actually going on in it? Why is everyone fleeing the cathedral except this one person we see from the back? Is there a vague shape hidden in the texture of the background? Is the cathedral… leaning a bit? Did Satan appear to the people? Did God appear (which I would find more frightening)? When you don’t know what’s going on in the picture, it’s more alarming and suggestive than the actual explanation probably is…