What the Bible says about Invisibility of Spirit
(From Forerunner Commentary)
A spirit being is invisible just like wind or air is to the unaided eye. The wind and the air are real, just as spirit beings are real, and they have substance just as wind does. But the unaided eye is not able to spot them, so the ability to see something that is spirit, or composed of spirit, is not in us by nature. Though it is not there naturally, the ability to perceive them can be given.
This is what Elisha means: "Give him the ability to see what is around us." And so the young man apparently saw a tremendous army of spirit beings who were ready to do battle in Elisha's behalf should anything occur. They were there all the while, invisible but nonetheless there.
John W. Ritenbaugh
Image and Likeness of God (Part Four)
When "spirit" is used in this sense, "air" is the closest physical thing Jesus could use to illustrate His instruction. Air is material, but it is invisible to our eyes, and its invisibility is what He wants us to focus on. Spirit is invisible—but immaterial—and in this specific sense, it has no form or substance. It is non-physical, but it can affect the around and the about, the environment, including a person begotten by means of it.
John W. Ritenbaugh
The Holy Spirit and the Trinity (Part One)Related Topics: Begettal of Holy Spirit | Begettal of the Holy Spirit | Holy Spirit | Holy Spirit, Begettal of | Invisibility of Spirit | Spirit | Spirit, Invisibility of