As per Vedanta, our true nature is the fourth, the Turiya, pure consciousness and bliss. As described by the Mandukya Upanishad, the symbol Om or Aum, represents the four states of our existence. Our waking state emerges out of our consciousness, moves to a dream state with our dream consciousness, to deep sleep, when the mind also shuts down and only consciousness remains , but it is in an unmanifest state. The quest on the path of spiritual enlightenment is to realise our true nature, i.e. consciousness in the manifest state. There are three main paths to reach this spiritual enlightenment – Bhakti yoga, the way of devotion, Raj Yoga, the path of meditation and Gyan yoga, the path of knowledge. While Bhakti yoga and Raj yoga are equally important, Vedas and Vedanta focus on Gyan yoga, the path of knowledge.
One good analogy to intuitively understand the concept that we are all part of the supreme Brahman, consciousness or Satchitananda, is to visualize the waves on an ocean. There are thousands of waves in the ocean, small waves, big waves, tiny droplets, big tsunami waves. If we look at these separately, we will see thousands or millions of entities, but if we look at these from the point of their true essence, water, then it is one water body. All the waves in the ocean are water through and through and nothing but water. As the waves crash against the shore, the waves die, but the true essence is not lost. The waves that crash on the shores are converted into foam or droplets , or might be evaporated by the Sun, become clouds , come down as rain, and reach the sea and become new waves again. In all of this their true essence, i.e. water, is never lost.
In a similar way, the entire universe and all entities, manifest in an ocean of consciousness, the Supreme Brahman, and we all are waves in this ocean of consciousness.