the "3 Essentials "..

Heaven, Man and Earth

Spirit, Mind and Body..

Chi, Essence and Nature..

but the 1st level is development of the Earthly "vehicle", the body.

No mater what level of spiritual development one strives for, without a healthy body, pain / discomfort and illness will continue to be a distraction and a deterrent from reaching higher levels of realization...

The Body/Mind creates unhealthy conditions and delusion that distracts the higher mind ..

The Sadhana is to maintain a healthy body, train the mind and transform the spirit so one can transcend the physical obstacles.

Then the Mind can become calm and clear and the Spirit can be light and vital, so Samahdi is attainable without ceaselessly fighting the physical...

Then man can unite with Heaven and Earth effortlessly