A belief system is everything we think we are and the world is about, without having a direct experience of. Our belief systems serve as a frame of reference in life that is not stored in the conscious mind. The conscious mind  is only capable of having one thought at a time, and belief systems  work in the background and belong to the subconscious mind. A very small part of a belief system is formed by the sensory information and the majority is based upon what we have interiorized and through education at home, school and even in university education. Some of it may come from past lives as conclusions we incorporated about life at the moment of death. Experience in life can support or defy an existing belief system until we need to exchange it and that includes religious, social, moral and scientific views about us and the world . But the most important thing in spiritual evolution is to let go and move beyond any belief system and see how those belief systems played a major role in our lives.

Even those beliefs that come from simple sensory information, such as a brick wall which is "solid" and prevents light from penetrating it, can be turned upside down. When we realize that it can be penetrated by just the same light or electromagnetic waves, but with a different wavelength of a common mobile phone, we understand that everything we "see" is just a small portion of the universe from a very small scale of frequencies. Unfortunately for most people and even scientists consciousness is something hard to percieve beyond the wall of our own mind. 

The most dangerous part of  a belief system usually concerns who we truly are and what the world is about.  When we learn at an early age that we are our bodies, thoughts and emotions, the fear of death already begins and conditions our lives.  Then when we are taught that there is "someone" who judges us, punishes and rewards us for what we think and do our identity shrinks and we learn to project a Divinity which is outside of us. It can take years or lifetimes to crack such belief system and still today, when science is built upon quarks, leptons and other elementary particles, most humans are not open to except anything beyond their visual capacity. 

Even spiritual belief systems that considered "advanced" like Non Duality can become an obstacle to deeper understanding when they blind a follower's mind and prevent him or her from seeing how their bodymind is a reflexión of their own consciousness. The mere idea of the Reality as Maya or ilusion suggests that  this world does not exist when it is excepted without questioning we can miss the beautiful experience of being a part of this gigantic hollogram and on the same time discover it's Source within us. Many spiritual teachers were simply not understood when reffering to the experience of the Source when their teachings were taken literally to be  saying something about the world. Nowadays, perhaps more than any time in history, it is important that we let go of any preconcieved approach to reality and begin experiencing it inside.