This poem comes from 1909 Mao Zedong's Four Musts: Changing Saigō Takamori's Poems to Father, and is adapted from the poem of Saigō Takamori, a famous military commander during the Meiji Restoration. The original poem is as follows:
The men are determined to go to the countryside,
If you don't learn to be famous, you won't return it.
Why bury bones in mulberry fields,
Life is everywhere.
-Saigō Takamori's poems
Literally, a good man is ambitious. In order to realize his ideal and ambition, he should not covet every tree and grass in his hometown, but should be at home all over the world.