Illusion of Reality
When looking at a physical object, we perceive that reflected light forms an image of that object on the retina of the eye. Through a complex detection process, the brain detects and integrates this data into a scene that appears in our consciousness. Though we have yet to understand how the image ultimately appears, we do tend to believe that it in fact does. We seemingly experience seeing, smelling, feeling the perceived form.
Considering the notion that what we think is real is actually a seeming perception then physical form is nothing more than something perceived in the mind because anything physical including your own body which houses your physical brain, is in fact a perception of the mind.
Some philosophize that the mind is something outside of the physical world and our experience here is a perception projected in our mind, thus creating the illusion. Put another way, we are dreaming the experience we appear to be having and it appears so real that we believe that it is. Our senses tell us that what we believe to be real resides outside of us, or, 'out there' around us.
The process of a spiritual awakening, then, is in a sense, the realization that what we perceived to be real outside of our selves, and our experiences that seemingly happen to us are all just a dream for which we can awaken from. All is actually one rather than separated parts we perceive in this reality. Deep in our subconscious mind the truth has been shut off simply out of fear of what true reality holds.
Bishop George Berkeley, an 18th Century philosopher whose primary achievement was the advancement of a theory he called 'immaterialism' and later referred to as 'subjective idealism by others, argued, 'only that which is perceived actually exists', which sparked a debate ensued as to whether a tree that fell in a forest actually made a sound. It wasn't yet known at the time how sound was transmitted through the air, or how the ear actually received the data. Today we understand a great deal more about the process and the answer has become a resounding 'no'. No sound is emitted by the falling tree in the physical reality, waves may pass through the air due to movement and pressure, but sound only exists as an experience of the mind of that which perceives the data.
Ultimately our reality is what our minds perceive it to be. Many may have difficulty grasping the concept, being that it goes against common sense, but the world resides within us rather than us residing in the world.