Explain that brothers should care about each other, because their parents' blood is linked together like branches. Make friends with the same interests, learn from each other and encourage each other in character.

[Note] Kong Huai: From "Poetry Xiaoya Long Beach": "The power of death and mourning, Brother Kong Huai." Later, "Kong Huai" was often used to refer to "brothers".

Cutting and grinding: this refers to the processing of jade and other artifacts, which is extended to learning.

Pro (zhēn): exhortation, exhortation.