Meditative concentration makes the body light and nimble.

Question: When I read the Kṣitigarbha Sūtra, I feel my body is very light and floating. Why is that?

Answer: This is a condition that arises in meditative concentration (samādhi). After the mind becomes still, the qi and blood flow without obstruction and circulate smoothly, so the body becomes soft and light, as if it had no bones. Spiritual practice should be taken up while one is still young; when the physical constitution is good, a slight calming of the mind gets the qi and blood circulating, and meditative concentration appears. Moreover, if a person's mind and thoughts are simple and have not been contaminated by much defilement, it is easy for the mind to become still and attain meditative concentration. In addition, if one has the mental conduct of a bodhisattva, has made aspirations and taken on responsibilities, and delights in helping others and practicing the bodhisattva path, then the merit one attracts and the blessing power of the Buddhas and Bodhisattvas both play a great role. For a person who has made aspirations and taken on responsibilities, after attaining accomplishment they will benefit more sentient beings, so the blessing power of the Buddhas and Bodhisattvas behind them is very great, and their own practice progresses quickly.
Those who have practiced for many years without progress should frequently examine what they lack in all aspects of their conditions, and remedy them as much as possible. If it is because they have not yet made the bodhi aspiration, they should contemplate the suffering of sentient beings more, contemplate the kindness of the Buddhas and Bodhisattvas and the kindness of sentient beings more, and harbor more gratitude and the wish to repay kindness. By enlarging the mind and extending oneself to others, making the bodhi aspiration will not be so difficult.

When meditative concentration appears, one will feel a separation of mind and matter, perceiving the unreality of matter, thereby discovering the truth and realizing true reality. When mind and matter are not distinguished, the mind will be obscured by matter, unable to discover the true nature of matter, and foolishness will not be removed. Discovering the unreality and untruth of matter is somewhat easier; discovering the unreality and untruth of the mind is extremely difficult. If one wishes to realize true reality, without meditative concentration there is nothing to speak of.

Even though one has gotten off the cushion and is no longer sitting in meditation, the mind still continues the state from within concentration. This shows that the meditative concentration of sitting can nourish the active concentration of walking, standing, sitting, and lying down, allowing the mind to abide in concentration at all times without scattering. Someone who gives teachings has said that the concentration of sitting meditation is useless, that people spend most of their time in activity, that sitting only lasts a short while, and that concentration disappears as soon as one becomes active. The facts demonstrate how absurd and baseless this person's words are. Not sitting in meditation themselves, they oppose everyone else's cultivation of concentration, understanding nothing about practice.