The sages teach us that before our eyes are many angles and demons good and bad, had we been able to see them we would go out of our mind, so God in his goodness hides them.
The story is told that a great Kabbalist who could see these things said that whenever the demons enter, it is through a doorway that the mezzusah is not kosher.
Countless stories are how God’s messenger the Rebbe who could certainly see these things as he would often instruct people to fix mezzuzahs though he was on the other side of the world and somehow one would find – even if he just bought new ones – that something was wrong.
The story is told of the holy Baal Shem Tov who banished demons who had made a nuisance of themselves and when the Torah scrolls were brought into the room they all left in a fright.
There are wavelengths that we cannot see, that are actually real, measurable and visible
Whenever you say the Shema for example you banish the demons of fear, whenever you say Ein Oid Milvado “there is nothing besides God” you immediately emanate a radiance that literally banishes all evil.
A great sage knowing the trick of Ein Oid Milvadoi escaped Nazi occupied Poland by repeating this continuously evading many near death moments for light banishes darkness.