Why don't we believe in things which are invisible for us?

To see is a question of perception. For example, in our body a lot of bacteria live. Only in our mouth we can find the great variety of them. They affect our teeth, and how fast our teeth deteriorate. But people don't hear any noise and even don't know about bacteria existence. These, in turn, don't see us. Impossibility to see the whole object, doesn't allow us to see it at all. Microorganisms see only objects which are directly in front of them.

Let's take another exmaple. Let's imagine that we are looking in a powerful telescope. It allows us to see the things which are in the distance of 4 milliard light years. Even if we know about the Universe, these knowledges are not enough for understanding the whole system of the Space.
It's because we have the equipment that doesn't give a whole image, just a part of it. *In order to see something, we need to see the whole thing. *

And we need to remember this quote when we are declining the spiritual things.
We can just see things which have their opposites. We see light because the darkness is. We see things of certain size which are good illuminated.
That's why live in this World with the open heart and mind. Be an openminded, honest and good person. And then you will see a new interesting anb beautiful things around you.