The core of Modern Spiritualism is based on the understanding that the universe is neither a static or created environment, but is itself both evolving and constantly changing. It is the fundamental belief of Modern Spiritualism that the purpose of the universe is to foster the evolution of spirit, through the mechanism of the evolution of life in all its forms throughout the universe.
This fundamental belief forms the basis for the three principles which are the foundation of Modern Spiritualism:
All things are but forms of energy and all energy is constantly changing form. Spirit is a form of energy that is evolving as a consequence of the evolution of life and the mind. Your spirit is part of the larger pool of all spirits of all living things.
The purpose of life is the development of spirit, both your own spirit and the spirit of all other living things. All life, spirit and energy are intertwined.
There are countless paths through life, you are responsible for choosing your own path by the decisions you make and accepting the consequences of your decisions. Happiness and spiritual growth are achieved when you walk your intended path, unhappiness and spiritual stagnation results when you stray from this path or let others define your path for you. Your spirit is constantly growing throughout your lifetime and will continue to evolve through many lifetimes.
Life exists as a vehicle for the evolution of spirit. To understand this belief you must first understand the ladder of evolution as defined by Modern Spiritualism:
Energy -> Inorganic Matter -> Organic Matter -> Life -> Mind -> Spirit
All matter, from the food we eat, to the ground we walk on and the air we breathe, was originally created when the forces of gravity and nuclear fusion in the stellar furnaces of stars and supernova fused the elements of hydrogen and helium into complex and heavier elements. These heavier elements of silicon, carbon, iron and so forth are what make up the earth today.
Our planet was formed by the same forces of stellar evolution that formed our sun. Originally lifeless, the complex inorganic elements the earth was formed from combined to create organic compounds and molecules over a period of billions of years. These organic molecules were the precursors of life, and eventually combined to form the simple, single cell creatures, that through the process of organic evolution, created the myriad of life that exists today.
As the web of life increased, so did the complexity of the life forms. As life evolved so did the development of the brain and the mind. With the evolution of more complex animals such as mammals, the brain also evolved to support the more complex needs of these animals, particularly primates, who were themselves evolving to survive in a rapidly changing environment. As the brain evolved and its capacity increased, so did the complexity of the social structure of the primates, ultimately leading with the evolution of Homo sapiens, to the world as we know it today.
Spirit is an outgrowth of mental evolution. As the life has evolved and expanded through the ages, so has the spirit - the spiritual and immortal part of man and of all living things. Your spirit (or soul) is a part of the continuum of life of your species, in our case humans. It is both you and a part of a larger community that represents all humans. Each new life is an incarnation of that spirit - while the body is mortal, the spirit is not, and your spirit grows and matures through the experience you gain and decisions you make in your lives.
Your reason for existence is to advance the evolution of your spirit. The decisions you make and the actions you take in this life, for good or ill, will shape and grow your spirit.
Your soul (or spirit) is the part of you that represents your spiritual nature. It is what guides you through life, the little voice or the gut instinct on what direction you should take or decision you should make. When your mind and body are in harmony with your spirit you will know it by the feeling of happiness and contentment that you have, because you will be walking the path that is right for you. Likewise, when you are ill, unhappy and discontented, it is time to reflect on whether you are really listening to your soul and conscience (the linkage of your soul and mind).
Everyone's path in life is different. When we allow ourselves to be led on a path defined by others (our parents, peers, church or society) instead of our intended path, we will be unhappy and stressed. Look inside yourself to discover if you are on the right path - not to what others are telling you.