This sentence is a famous saying in ancient China, which means that people who are good at talking about heaven must find their roots in personnel, and those who are good at talking about people must also find their roots in heaven. It emphasizes the relationship between heaven and people, and the need to pay attention to the root causes when talking about heaven or people.

Specifically, people who speak of Heaven should look for the essence of Heaven from the aspect of personnel, because Heaven will eventually affect human nature. For example, weather changes will affect the growth of crops, and then affect people's lives; The movement of stars in the universe affects the time change on the earth, and then affects people's lives. Therefore, in order to understand the sky, we must first understand its influence on human beings, and we must also understand its influence on the sky.

Similarly, people who talk about human nature should find their roots in the sky. Human beings live in nature, and changes in the natural environment will affect human life and production methods, and human life and production methods will also affect the natural environment. Therefore, if you want to understand human beings, you must first understand its relationship with the natural environment. If you want to understand the natural environment, you must first understand its relationship with human life.

In a word, this sentence tells us that when we talk about heaven or people, we need to focus on the root causes, and we need to understand the relationship and essence between them in order to better understand and master them.