There are no proofs of anything spiritual, only beliefs.
I agree in part. The essence of Spirit is not any “thing” or experience thus it cannot be measured, demonstrated or proven. When considering Spirit the only verb that can approach it is the verb to be. This perspective has the potential of bypassing the conceptual mind and gives you a chance of “realizing” Spirit’s True Nature directly. The idea of Spirit, or the Natural State, is a mere empty concept otherwise.
The moment we objectify Spirit or The Natural State as a concept we set ourselves separate from it in our minds, and that is the basic imagination that keeps the seeker seeking and is obliterated when realization occurs. The way to realization can never be through trying to understand Spirit conceptually. A different approach, a specific type of inquiry, is required from the ripe seeker.
As for beliefs, Spirit is ever available, present and “realizable”. Therefore, for some people Spirit is not a belief or a mere concept. In realization all of our previous beliefs about who I am (or you are) vanish. We see ourselves for what we are and others for what they are. Not merely the personality, not even a soul, but Spirit.
This is not some grandiose state; it is the Natural State of a human being. A three-year old lives like this. Our minds simply have been filled with wrong ideas and negative emotions in the course of our “education” and conditioning in life so that we have lost sight of what is Natural.