What is the central idea of Lu Xun's Brothers? What is the function of "an unknown man died" at the end of the article?

I only came into contact with this article recently. There are many things I don't understand, and there are many doubts in this article. I wonder if it's Jingfu's body or Hesheng's body? First of all, this is his dream. Secondly, he arrived at the public security bureau later than usual. Then he asked himself to handle the case. What did he finally feel at ease for? Of course, I don't quite understand. The central idea must be to criticize the ugly face of the people. When Jingfu was sick, his first thought was livelihood, which shows that the feelings between brothers are linked by interests. But what profound meaning this topic hides may only be understood by Mr. Lu Xun himself.