Xi 'an's old man is a sketch lover. After the outbreak of the epidemic, he saw the greatness and hardship of medical staff, so he wanted to record their greatness and hardship through painting. I think this is a very meaningful thing in itself, because medical staff are really hard, and they need some ways to let everyone know what their work is like and what they are trying to do. The old man noticed this and took it as the object of his sketch. I think this behavior itself is quite meaningful. He paid tribute to the medical staff by recording their portraits at work, because he said that the medical staff were really hard and great, so he wanted to record it by painting, so as to record this history.
Judging from these images, I think the old man's paintings are also very good. His painter is very good, his paintings are lifelike, his lines are smooth, and he does draw a lot, which shows that he can persist in doing this. Moreover, from his photos, we really see that the ordinary work of medical staff is really tired and hard all day. This is what I think this sentence means.