Confucius said, "Review the past and learn the new, and you can be a teacher with this."
So old: just (bearing) can: can: rely on: into.
There are four solutions to "review the old and learn the new". One is "review the old and learn the new", and gain new insights from it. The second is to "review the past and learn the new": on the one hand, we should review the stories of laws and regulations, on the other hand, we should strive to acquire new knowledge. The third is to review the old and learn the new. With my rich experience and improved understanding, I can always learn more from what I have read before. Fourthly, I think the correct explanation means that we can foresee and solve future problems by reviewing history. This is the ability that a real master should have.
Combining these four solutions may be more complete: within your ability, read the classics as widely as possible, think over their meanings repeatedly, and review what you have heard regularly, so as to gain experience and understanding; And strive to absorb new knowledge; In this way, we can expand the field of human knowledge, and closing the door can also give the sages the meaning of the wisdom era. Such a blend of old and new, ancient and modern, can be called "reviewing the old and knowing the new, being a teacher."
Some scholars believe that it is not appropriate to review the past and learn the new, because literally, only absorbing ancient and modern knowledge without understanding experience is like a buyer and seller of knowledge, not a teacher. Then let's take a look at the meaning of "teacher": in the Analects of Confucius, there is the word "teacher" in chapter 14, which has the same meaning as today's teachers, except this chapter, there are three chapters.