What is yoga it is difficult to attain the level of samadhi until we can connect with ourselves. It is not just exercise but science-based physical activity. In this the brain body and soul meet each other. At the same time there is a harmony between human and nature. It is a way to live life properly. Sri Krishna has also said in the Gita that Yoga Karmasu Kaushalam means that yoga brings skill in actions.
It is wrong to tie yoga in the realm of religion faith and superstition. Yoga is science which is the art of living life. Also it is a complete medical system. Where religion binds us with pegs yoga is the path to freedom from all kinds of shackles.
When you learn to hold the entire body properly you can feel the energy of the entire universe inside you. This is the sum.
That is to stop the mental instincts from becoming fickle. In easy language yoga is not to let the mind wander and keep one place stable.