The third paragraph points out that ancient sages attached importance to teaching with examples, and further expounds the necessity of teaching and the truth of taking ability as a teacher.
function
Everything in the world often exists in comparison. "Only contrast can distinguish". Once two things are compared, we can tell the difference between them. Therefore, in argumentative writing, the method of comparative argument is often used to compare two contradictory or opposing things and reasons from both positive and negative aspects, so as to reveal the essence of things and make the things expounded more profound and convincing.
Contrast between true and false, you can go from false to true; The contrast between good and evil can suppress evil and promote good; Contrast between right and wrong can set things right. Therefore, the use of positive and negative contrast argument is more powerful and clearer than just reasoning from the front. In particular, topics with comparative factors, such as thrift and luxury, taking and giving, contentment and lack of knowledge, are all suitable for writing in this way.