Being willing to be a weed and waiting for the fire to burn in the ground means: serving the people silently and dedicating oneself.

This sentence mainly praises Lu Xun, and it is a metaphor that Lu Xun is willing to contribute everything he has to the revolutionary cause.

Source: "Some People" by Zang Kejia.

Original text (excerpt): Some people are willing to be weeds, waiting for the fire underground.

Some people live so that others cannot live; some people live to make a better life for the majority of people.

Understanding:

The understanding of this sentence is that I would rather be a weed, waiting for the underground fire to burn, than make some unnecessary sacrifices.

Describes a person who is willing to sacrifice himself in very small circumstances rather than lose his moral bottom line. In fact, such a character is particularly worthy of our learning. We are most important in life. The important thing is to stick to your moral bottom line.