"Living by the qi of heaven and earth" means that the human body lives by the material conditions provided by the qi of heaven and earth;

"The law of the four seasons: it means that people have to adapt to the law of yin and yang changes in the four seasons in order to develop and grow."

English translation of these two sentences (Paul U.Unschuld version):

Man obtains life through the qi of heaven and earth;

He matures according to the laws of the four seasons.