The ordinary person's vision is blocked by the physicality of his own existence.
To achieve anything spiritually meaningful, a person has to have reached a certain rung or level of consciousness beyond the physical.
Otherwise, there is simply no possibility of making the contact that could enable one to understand what he is experiencing.
Just as children, and even many adults, can grasp only so much of a work of art and no more, especially if they are untrained.
They can come into physical proximity with it, see or hear it, and respond according to their individual levels of understanding.
Just as recent experiments on the process of observation in animals disclosed that they distinguish only moving objects.
Not that an animal fails to see an object that doesn't move, it is simply alerted only by the exterior stimulus.
And so it is for all creatures; the ability to grasp the reality of a situation depends on the level of consciousness of the one experiencing it.
As human beings, we are unable to perceive various spiritual entities, and only by the performance of the mitzvot, or its equivalent, is a relationship established.
Whether one will feel this relationship with the spiritually invisible depends on one's level of consciousness.
An ordinary person is usually unable to do so beyond a limited extent.
Thus, for example, it is maintained that in the Land of Israel there is a greater concentration of holiness.
If, as not infrequently happens, someone complains that he is not aware of any more holiness in Israel than elsewhere, the answer is that he himself is to blame–not the Holy Land–that he should work on himself and repent and try to make himself a more effective receptacle of spirit.
The perception of holiness belongs to the perceiver as well as to that which is perceived.
Just as the same book can be profoundly meaningful to one reader and be utterly meaningless to another, the same place can be holy to one person and commonplace to another.
–Rabbi Adin Steinsaltz
From The Long Shorter Way, p. 320, by Rabbi Adin Steinsaltz