Updated: Apr 3, 2022
Feb 9, 2021
The spiritual realm is not different from the material realm. The human eye and the process of perception resolve it into what we call the material world. Remember the principle -
The universe is not what it looks like. It is merely resolved that way.
The universe is really spiritual or some sort of flux of energy. It looks material/physical because it is resolved this way. Compare it to an LED TV. Images on the screen are really not people or things. It's all just a light show of LED bulbs that gives off an illusion of physicality.
Things, people you see are really spiritual in nature. Your eyes create the illusion of solid material things. So why can't you pass through them? Because they have their properties. Electric field lines cannot pass through conductors. Flies can't fly through a stream of air. Fast-moving air is impenetrable to them, not for us though. Similarly, changes happening (the flux) in walls make them impenetrable to humans. Wifi and Bluetooth can still penetrate them though.
By the way, what if I tell you you don't have to interpenetrate because you are already in them and through them. You don't want to penetrate your leg because it's already your body. It is crazy to think you want to penetrate objects that you are already deeply interpenetrated with. You are a spiritual union of everything. There are no hard lines of separation. Think of point charges. Their electric fields are already deeply interpenetrated. They were never separate things, to begin with. Think of the superposition principle in physics.
Imagine a deeply connected set of computers. You see them as separate things because you can't see the wifi traffic coming in and out of each of them; the human eye can't see radio waves. You can't see they are all one. You only see what is visible in what we call "visible frequencies". You call these objects materials or physical. This is how the universe is too. Everything is deeply interconnected and interpenetrated. The eye resolves them as independent and individual things by selectively perceiving some things and rejecting the rest.