Because this is a symbol of knowledge, "Zi" has this meaning. It is an honorific name for people in ancient times. It is called a teacher or a moral and knowledgeable person. So this word was very meaningful in ancient times.
In ancient times, especially in the pre-Qin period, the word Zi was often used as an honorific. For example, we are familiar with the nobility system of the Zhou Dynasty, where the duke, prince, and son are male. In ancient times, it was an honorific title given to men. For example, in the state of Chu, although he himself became the king, he was still known as Chu Zi among the Central Plains princes and Confucians. In short, the king of a small country and the high officials are all called sons.
The word "zi" was later extended from being reserved for venerable people to also being used by moral people, that is, adding "zi" after the surname to show respect. Such as Confucius, Laozi, Mozi, Xunzi, Gongyangzi, etc., but the meaning of this word is equivalent to the current respectful address of a person as Mr. The surname is preceded by the character "zi", such as Zilu, Zigong, etc. This character "zi" means my teacher, and is the honorific title given by the descendants to their predecessors.
In the Analects of Confucius, it is recorded that when Confucius said that his disciples were all called Hui, Ci, You, etc., the word Zi was not used. When recording what other disciples said, the word Zi was added before the surname to express respect for the teacher. However, because of Yan Hui's high status, he did not add Zi before his surname. Instead, he added Zi after Confucius, Mencius and Zhuang. When the word "zi" is used alone, it means what you mean today. For example, in the Book of Songs, if I don't go, "Zi Ning Bu Si" sounds, this word "zi" means "you".
It can be seen from this that the word "子" is a respectful title for the ancient powerful sages. For example, Lao Tzu is the founder of Taoism and a very influential person at the time. Lao Tzu's real teacher Li Er, in order to show his admiration for him, he respectfully called him Lao Tzu.
Including Confucius, whose real name is Kong Qiu, the founder of the Confucian school, he is definitely a great sage and great sage. It can be seen that those who can be called Confucius are all great sages at that time. All are influential people.