I'm reading The Turn of the Screw by Henry James, and I've found it difficult to understand the meaning of the sentence pasted below. I suppose it can be roughly paraphrased to "I was monstrous, and ready to pronounce it that the child should be under an interdict"(if I made a mistake in the paraphrasing, please tell me). The points I want to know are "the function of the it before that-clause" and "the meanings of the that-clause and the whole sentence".
I'd appreciate it if you would answer my questions.
We met, after I had brought home little Miles, more intimately than ever on the ground of my stupefaction, my general emotion: so monstrous was I then ready to pronounce it that such a child as had now been revealed to me should be under an interdict.
These sentences are quoted from the beggining of Chapter 3, and the text is from this site(https://www.gutenberg.org/files/209/209-h/209-h.htm).