What do Du Fu mean by "master" and "poet"?

Du Fu's title of "Poet Saint" is Poet Saint. There are many comments on Du Fu by predecessors, the most important of which is that he is a master of poetry. Master was originally the concept of sage in the middle of Confucian terminology, because this is what Mencius said about Confucius, and Mencius said that Confucius was a master. At the same time, the Song people also said that Yang Wanli said Du Fu was a poet, which meant that he became a saint in the field of poetry.