"When he came to get [the] hog I gave him enough wire to patch up his pen." (3)
This is Harris talking. By giving Abner free wire, he's accusing Abner of being below him in terms of social and economic class. A high-class guy like Harris would never leave a fence un-mended, and can always afford to buy wire. By giving Abner the wire he's showing Abner that Abner needs his charity, and his advice. Harris's burned barn is evidence that Abner didn't take kindly to the suggestion.
In the early afternoon the wagon stopped before an unpainted two-room house […]. (32)
If we weren't sure the Snopes were poor before, we are now. Imagine how cramped a two-room house is for a family of seven. As we learn in the rest of the paragraph, this is what they have always lived in and always will, unless they can somehow change their position in society.
"Pretty and white, ain't it?" he said. "That's sweat. Nigger sweat." (46)
Abner strongly suggests that de Spain's mansion was either literally built by slaves or by low paid black workers, or from the profits of work done by slaves or low paid black workers. This gives us a hint of why Abner has it in for de Spain.