If we are fortunate enough to practice a summer practice period before our dewlike life drops down, whether in the realm of humans or devas, we will surely replace our skin, flesh, bones and marrow with the skin, flesh, bones and marrow of buddha ancestors.
During every practice period it is the Buddha ancestors who come to practice with everyone, and everyone who participates in the practice period practices as a buddha ancestor. Because of this, those who engage in a practice period are called "one thousand buddhas and ten thousand ancestors." The reason for this is that a practice period is the skin, flesh, bones and marrow, as well as the mind, consciousness, and body of the buddha ancestors. Practice period is the top of the head, the eye of the fist, the nostrils, and the buddha-nature circle drawn in the air, as well as the whisk, the wooden staff, the bamboo stick, and the sitting mat of buddha ancestors. Practice period is neither creating something new nor reusing something old.
The World-Honored One said to Complete Enlightenment Bodhisattva and all those in the assembly as well as to all beings:
"Those who participate in the three-month summer practice period should abide as pure bodhisattvas, their minds free from the world's chattering, uninvolved with the world's opinions. On the opening day of the practice period, make a statement like this in front of the buddha image: I —Monk, Nun, Layman, or Laywoman so-and-so — now mount the bodhisattva vehicle in order to activate the practice of tranquility and together with all beings enter the mark of purity and abide in it so that we can all make complete enlightenment our temple. [...]"