The Good Earth has many memorable quotes that can be used to expand upon. Here are a few with some notes.
"There was only this perfect sympathy of movement, of turning this earth of theirs over and over to the sun, this earth which formed their home and fed their bodies and made their gods."
This quote is from the early chapters where Wang Lung is working on the farm. His feelings of being connected to life through it is what helps him through the harsh realities of his life. These are lessons that he takes with him when he leaves, and lessons he tries to pass on to his sons.
"Sell their land! Then indeed are they growing poor. Land is one's flesh and blood." Chapter 5, pg. 37
This, again, shows the connection to the land and how Wang Lung views everyone through the yardstick of land ownership.
"I must stick a little incense before those two in the small temple. After all, they have power over earth." Chapter 15, pg. 103
This shows how superstitious and cautious he is when it comes to his life and his farm. If the gods are real, he reasons, then one must keep them happy.