Statesboro, GA, USA
What is the reason for 'brain' and 'soul' to be divorced?
More like married than divorced. And yet despite its oneness or harmony, marriage still requires functional separateness.
And yes, we're talking figuratively, and all metaphors are limited, even if helpful.
How is it that mere molecules can affect the 'soul' of a person if the soul is an extrinsic entity?
What do you mean by extrinsic? Who ever said the soul was hermetically sealed or completely separate from our physical organism? Not I.
Distinction and Union coexisting is not that difficult to imagine, especially seeing that there are instances of it all around us. Just think of the relationship between human body parts which affect each other, and yet maintain a kind of separation.
Again, metaphors ... limited but helpful.
If I drink a bottle of Jack Daniels does my soul get drunk?
I'm not sure what you mean. I suspect you're just attempting a reductio ad absurdum. But if we have a soul and a brain, there's no need to assume that their nature is identical. The opposite error is to assume that they have no relationship at all.
If you put gasoline in your car, do your wheels catch on fire?
Separate, yet intimately related.
Why does the non-natural soul need the natural habitat of the human species? Why can't it dwell equally in a two-by-four or a door-stop? And, if it can -- then why have the species at all?
You are asking questions which involve teleology. Such conditions defy logical necessity by their "Is-ness". The relationship between a natural body, and a spiritual soul, is not one born out of need, but of design. And if you think about it, many things fall under this category. Why did my son think blue goes so well with yellow in his picture hanging on our fridge? Why is the sky blue? Why Why Why?
Or you may think of it this way. Yes there is necessity, but it follows and is subservient to design. In the design itself is an element of pure arbitrariness that can't be escaped. (That much is true whether you believe in God, or atheistic evolution).
G.K. Chesterton put it this way:
"There are certain sequences or developments (cases of one word following another), which are, in the true sense of the word reasonable. They are, in the true sense of the word, necessary. Such are mathematical and merely logical sequences. We in fairyland (who are the most reasonable of all creatures) admit that reason and that necessity. For example, if the Ugly Sisters are older than Cinderella, it is (in an iron and awful sense) necessary that Cinderella is younger than the Ugly Sisters. there is no getting out of it. Haeckel may talk as much fatalism about the fact as he pleases: it really must be. If Jack is the son of a miller, a miller is the father of Jack. Cold reason decrees it from her awful throne: and we in fairy land submit. If the three brothers all ride horses, there are six animals and eighteen legs involved: that is true rationalism, and faryland is full of it. But as I put my head over the hedge of the elves and began to take notice of the natural world, I observed an extraordinary thing. I observed that learned men in spectacles were talking of the actual things that happened- dawn and death and so on, as if they were rational and inevitable." (From "The Ethics of Elfland", Orthodoxy)
So, no there's no logical necessity of God conjoining a soul with a human body in creating someone who is more like himself than anything else in nature ... but there is a kind of artistic necessity involved in that he chose to do so. Only after that fact, does it become an ontological necessity.