The Relationship Between the Physical Body and the Four Great Elements

Time is a wondrous false dharma. If a person could fly to the heavenly realm, stay for a few minutes, and then return, hundreds of years might have passed in the human world—several lifetimes of human lifespan would have gone by—yet this person would still be as young as before, not aged at all. Why is this so?
Whether one ages depends on the physical body. The physical body is composed of particles of the four great elements; through arising, ceasing, and change, the body continuously matures, develops, and transforms. The four great elements constitute the qi and blood needed to sustain the physical body. If the qi and blood flow vigorously and the body receives ample nourishment, it does not easily mature and age, and the person appears young. Qigong and various cultivation practices can all make the qi and blood active and circulating, nourishing the physical body, so those who practice well generally look young. Time reveals the arising, ceasing, and change of the four great elements: the longer the time, the more evident the arising, ceasing, and change, and the more mature and aged the body becomes. In short, youth and aging lie in the development and transformation of the organization of the four great elements. 

Why do the material bodies of devas not age? Because the composition of the four great elements in a deva's material body differs from that of a human body. The four great elements of humans are coarse and heavy, while those of devas are subtle and refined. Devas can fly, but humans cannot. After a human ascends to the heavens, in accordance with the living environment of the heavenly realm, they absorb the subtle particles of the four great elements there, and the four great elements of their material body will also change, so the body becomes close to that of a deva. When a deva comes to the human world and absorbs the particles of the four great elements of the human world, the material body draws closer to that of humans; the four great elements also change, becoming close to those of humans. For example, when a deva of the Ābhāsvara heaven of the second dhyāna comes to the human world and eats the flavor of the earth of the human world, the four great elements of the material body immediately change, and the deva can no longer fly freely and cannot return to the heavens. 

When qi is full, one does not think of food. Qi is a form of material energy composed of the four great elements. After sitting in meditation and cultivating samādhi until the qi is abundant, one no longer feels hungry and can eat little or nothing, and the body feels light and comfortable. Because the four great elements of qi differ from those of food and drink—the four great elements of qi are subtle and light—abundant qi can make the physical body float and rise, while the coarse and heavy four great elements of food and drink make the body heavy. Therefore, eating less and cultivating samādhi more will make the body healthier. No matter how nutritious food and drink may be, they are still coarse material form (rūpa), not the best thing; their nourishment is not as good as that of qi.