As for the mechanism that we cannot see into the spirit realm is a mystery.
I believe this is not a mystery, when all the pieces of the puzzle are correctly assembled.
The piece by G.H. Palmer identifies to me the common problem that needs to be overcome in order to understand the problem which solves the mystery.
Palmer notes,
"Under our analysis two antithetic worlds emerge, a world of nature and of spirit, the former guided by blind forces, the latter self-managed." Here is an ontological ambiguity which never leads to the truth, a view quite predominant in Christian thinking to this day, IMO. Basically, the notion that spirit is intrinsically different in structure (meaning wholly good, alive or cleansed) than matter, what we Christians often call 'the flesh' is the error that has to be overcome in order to see the truth.
I won't get into the problem areas caused by improper assignment of a whole state of 'goodness' to human spirit, but can provide a link to my web site for further reading of an article I wrote some years ago in case anyone wishes to push the matter to clarification. The way I think of it is kind of abstract, but quite logical and lines up well with Scripture.
1) All that exists in information...matter, mind, spirit, etc. All information exists (here's the important ontological distinction) in possession of some ratio of the proerties
true and
false.
2) Truth and falsity manifest themselves in different ways in different things, but at base they share in common the fact that to the extent an informational structure is true, it's perfect....to the extent it's false, it's imperfect. In the realm of matter, we can say that the structure of a home is nearest perfection when it's new. If the home's purpose is to house humans safely and comfortably, then the home has a high degree of truth in its true/false ratio. One hundred years from now when the mutability of time has ravaged the house, it will have fallen into falsity or imperfection to the degree that it no longer is capable of housing human safely and comfortably.
3) In human intellect, there's a very different nature than is found in simple matter because spirit as an animating force exists as the most important part of the whole....spirit infuses matter to create mind (intellect). I agree with Palmer's observation,
"When the Renaissance revolted against the teachings of the mediaeval church, the disposition to return to nature was insolently strong." The move toward a materialistic worldview automatically assigns relevance to the material world and dismisses the notion of animating spirit, which clear paths for teachings like evolution and etc.
I digress. Truth and falsity take on a new dimension in created intellect that isn't found in matter. Here,
true metamorphoses into moral "good" and
falsity into the moral evil of wickedness. Spirit blends with matter [brain; sense data] to form intellect, from which reason springs. Reason is used (both before and after) in forming intent, and the will is a product of this process. The mystery IRQ speaks of is solved in understanding that the extent reason is corrupted by falsity is directly correspondent
to the degree to which both matter and spirit are corrupted by falsity.
The idea that spirit is clean and the human nature of attraction to and appetite for evil lies in matter is an untenable and illogical conclusion. In intellect, spirit as animating force is the primary force. Think about it...if spirit were wholly pure and regenerate, the falsity of matter (brain, body) would have only a slight effect on the cognitive process. Thoughts would be very close to pure. The true and good have unity with truth; falsity has a natural association with evil. The wholly "clean" state of spirit is the primary force of human intellect...to say that some ratio of falsity in matter is able to predominate over spirit in intellect is simply irrational.
Now if you move falsity to
both spirit and matter, the whole picture becomes coherent and realistic. Experience is full of both good and evil in some real proportion to one another. The devil doesn't make us do it, though he certainly encourages us...but we perform evil from a true evil nature, a nature that is intrinsic to all of our being, spirit and body.
The mystery disappears when we understand that tension and resistance exist between the antithetical properties tue and false. Falsity in spirit creates an intellectual "darkness" of understanding spiritual things. We love our darkness (falsity; evil...Jn 3:19) because falsity resists spiritual truth, it's not in unity with it. Spiritual absolute Truth (Christ) is actually the means of death (thus providing a high degree of tension and resistance) to human falsity. We don't want to die, so we hide in our darkness...this is why we don't understand spiritual things.
Sorry this is so long, but it's hard to explain this in two or three sentences.