Understand that ancient scholars compared similar things. The sound of the drum is not equivalent to one of the five tones, but when an instrument is played, there is no harmonious rhythm without the drum; The color of water is not equivalent to any of the five colors, but when painting, the five colors are not distinct without water; Learning does not mean that you can be an official, but an official can't do a good job without learning; Teachers are not equivalent to any kind of relatives in the five clothes, but if there is no teacher's instruction, their feelings are not close.
? Zheng Xuan's note: "Take things as they are. Ugly, you are better than me. " In ancient times, pentatonic refers to the sound of nature (there are no 4 and 7 tones now). If you can't sing, you say that you are tone-deaf. Through the analogy of drum, water, learning and teacher, this chapter draws inferences and bypasses one by one, and then explains that drum, water, learning and teacher are equally important in different categories, but it is to highlight the importance of teachers.
? Earlier, we talked about "learning is nothing to the five senses, and the five senses are incurable", telling us that learning is very important. "A teacher is not equal to five clothes, and five clothes are not close" tells us that teaching is very important. "Xue Ji" means learning to teach. Learn what? Learn to teach. If you can teach, you will learn, and if you can learn, you will teach. The Book of Learning is drawing to a close. It tells us by comparing ugliness with things that learning and teaching are our foundation, and it is also the foundation for us to achieve ourselves and be happy in life. Learning to learn and teaching to teach can really benefit mankind.
? Mencius said, "man and beast have a few hopes." The difference between man and beast is very small, and learning and teaching are the most fundamental differences between man and animal. If people don't learn, they will easily be no different from animals. If there is no "teacher" to teach us, we will also degenerate into animals. Therefore, Xue Ji tells us that "building the country and the people, teaching first". Learn first, teach first, and pay equal attention to teaching and learning.