What is Samadhi?
Samadhi is not becoming one with who you are, i.e. the soul. It is knowing who you are i.e. the soul different from the body.
Yama is about our social conduct. Niyama is our personal conduct. Asana we all know is about the container of the Soul i.e. body. It keeps the body (including 5 sensory organs and limbs) fit and disease-free. Pranayama helps us taking control of the mind.
Once our focus moves away from the body and mind, our inward journey starts with Pratyahara.
All these years and all these births we have identified the self with the body. This is the biggest myth. To know the real self, our myth must be broken. Yoga helps us in doing so. Once your focus is away from the body, the real self is enlightened.
When we see a mesmerizing scene or when we are gazing at a sea, sunset we ignore our body and become one with the situation. This is Dhyana. When we do it for some time unceasingly it becomes Dharana.
When we focus on any object for Dharana we achieve Sabija/ Savikalpa (with seed) samadhi. When there is no object, it becomes Nirbija/ Nirvikalp (seedless) samadhi. This is an advance stage of Samadhi.
Dhyana and Dharana gradually help us ignore the seen (body) and experience the seer (Soul). This is in a real sense the final state and objective of Samadhi. Our soul has never reached this state ever in any of the previous births hence this cycle of life and death has remained ceaseless.
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Once you achieve this state and experience the real self-i.e. Soul different from the body, that is the beginning of the end of the cycle of life and death. This is why Samadhi is significant. This is what an advanced practice of Yoga can do to us. This is not the state of Moksha but puts the soul on the path of Moksha.
If you do Asana and Pranayama you call yourself a Yoga practitioner. You are on the right path. But this is just a base camp of Mount Everest. As a Yoga practitioner, your real target should be reaching the summit of Mount Everest i.e. Samadhi.
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