According to Paul, the mind of a christian can psychically fixate on the spirit OR on the flesh. In other words, at least one part of the human soul has the ability to focus an awareness of both (or perhaps, either) the physical and spiritual realms. Also according to Paul, apparently, the mind of a spiritual person has the ability to defend its own psychic domain against the suggestive input of evil spirits. (For two unique examples, compare Eve & Jesus). However, I know of no account whereby human bodies or souls have ever been able to affect the physical or spiritual realms directly (at least, not apart from special, divine circumstances; see * below.)
Can spirit affect spirit? Presumably, yes. The scriptures allude to fighting between angels and also speak of God [who, remember, is Spirit] having conversations with Satan. However literally we are supposed to take such accounts, the relevant aspects of what they represent are clear enough. Spirits can interact with one another. So then, to questions of tangibility: What is a human spirit? What can it sense, "touch" or affect? What else can it do, if anything? In what realm(s) does it operate? Most of all, what has God intended as its proper function, in our lives?
Let's assume our spirit is like other spirits in at least the following ways: spirits are invisible and intangible, but tangible to other spirits. Or perhaps more accurately, for a christian, tangible to the Spirit of God. (*** Those poor 'unregenerate' souls in the Gospels who were demon-possessed, in my understanding, had not yet been born from above. But after the Lord's resurrection, a christian's warfare against dark spiritual powers seems to be chiefly mental, and defensively so, suggesting that the weapons of the enemy against a spiritual human being have been reduced to indirect mental suggestions, volitional temptations and emotional disturbances. In other words, these evil spirits continue attacking our souls.
In this conclusion, I have to stop short of suggesting that no demon can possess a 'born-again' christian, partly because that would be tantamount to labeling such self-reported victims as false believers or liars, and partly because for all I really know we cannot totally rule it out. Suspending judgment for these reasons, I might suppose a demon could possess a christian whose human spirit was so functionally anemic as to be a non-factor in the event. That's still insulting, but it is neither condemning nor exclusive. Nor is it over-reaching. ***) All of that small print was very important, but we have now said well more than enough about darkness.
This understanding also suggests that Old Testament patriarchs like Abraham and David did not have spiritual relationships with God, but developed extremely intimate yet purely soulish relationships with Him. That, by the way, is not an insult. That is a compliment. We have very few such people on record, before Jesus, who devoted much of themself to the Divine One. [So how did they "hear" Him? Perhaps God spoke audible whispers on a subliminal level, generating tiny sonic vibrations deep in the inner ear, much smaller than those at Jesus' baptism and transfiguration.(?) Or perhaps God is psychically telepathic, whenever He wants to be.(?) Whichever the case, the laws of physics leave us with the same basic options for angellic visitations to Abraham and Daniel. Divine dreams, of course, classify as telepathy - as odd as that is to say!]
I'm not really worried about explaining the patriarchs or their contemporaries. Somebody could posit that God indwelt David or Abraham, but I sure don't see it. Further, I think such positing tragically redefines spiritual co-habitation with God as a metaphor for soulish, unidirectional devotion (which necessarily becomes superstitious in receptive spirituality, unless prophets or miracles come into play very often). Such theoretical, homogenizing whitewash also sticks christianity into those Old Testament methods of interacting with God. That much of christendom honestly thinks this is supposed to be the way of things is incomprehensively tragic.
No matter how we understand the interaction of Old Testament devotees with the Divine One, the New Testament is very clear that the new creation, this new indwelling intimacy - which is to say, this spiritual intimacy - is something entirely new. According to the New Testament, this human spirit is exclusively given to christian believers, and by all accounts, this spirit seems to be given for one purpose - so that we may interact with God on his terms, spiritually.
To be continued...
*In the Gospels, casting out demons seems to be a matter of outward, spiritual power. Jesus shared such power at times with his disciples. OT examples differ widely: Balaam's donkey was briefly given spiritual sight by God and Elisha once demonstrated the power to make iron become buoyant. However, such earmarked grants of power by divine intervention should not be taken as normative. Spiritual power seems to come and go, but the current inquiry is about inward, spiritual being.