Caution! Some of this maybe considered spoiler material.
OK, first the easy one:
The book is divided into three sections:
I - Fiat Homo (let there be man)
II - Fiat Lux (Let there be light)
III - Fiat Voluntas Tua (??)
Now, what does Mrs Grales and Rachael represent? (She is the two headed lady in the third section where one head goes to sleep and the other head wakes up.)
I know that Rachael is born without original sin, but I guess I think that there must be some deeper symbolism it implied about the post-post-apocalyptic world.