Think about the dreams you have while sleeping. You always have yourself in the dream. It doesn’t matter what the contents of your dreams are, there are always two entities i.e. you as a subject and everything else as an object. In the dream everything you do is very real to your dream self. In the waking state you know these are dreams and illusions. But in dreams you do not know that you are dreaming and assume everything to be real. Even if you see an elephant flying or random people popping up and disappearing you never question to yourself why did this happen? In dreams if someone throws a stone at you, you get hurt. You see in your dreams everything is real to your dream self. But what about your real self? It is totally unaffected, even by the apocalypse in your dream. If you notice you will find that your dream self is not different from other objects of your dream. It is because you entire dream universe is the construct of your mind. So any object such as the trees, people, animals, buildings, sea, whatever you see in your dreams is the same as you as the subject. There is no difference at all because everything is created by your mind. Everything will die once you wake up. In dream you experience stress, pain, fun, happiness and all sorts of things but are they real? Say if you eat one candy while awake and three candies while asleep. Can we say you ate 4 candies? No because 3 candies were just a dream an illusion. Even though these dreams appear very real upon waking up we realise it was all an illusion.
Now think about your waking life as a dream as well. Even though you the subject and everything else the object appear different they are actually the same, just like the dream. As in dream we are not conscious that we are dreaming, similarly in a waking state we are not conscious of our true nature. Think of this universe as unlimited consciousness, just like your mind. Entire universe is nothing but consciousness without boundaries. As your mind can image practically anything this ultimate consciousness can produce anything. Anything this consciousness produces is no different than any other form. For example a necklace and a ring may appear very different objects but they are gold. Similarly this universe and everything in it is made up of consciousness. Even if they appear different they are the same. You are the universe, realising this is called enlightenment. Knowing yourself as this consciousness is enlightenment. Consciousness is beyond mind and body and any other matter. Consciousness is unaffected by anything is beyond birth, death, time and space. Universe rises and dies in this consciousness. We identify ourselves with mind and body. When we realise this mind and body appears and disappears in the consciousness, and that our true nature is that consciousness we are enlightened. In Vedas this realisation is stated as Tat Tvam Asi or that essence is you.