What point does Steinbeck make about qualifications for ownership?

The following quote says it all;

"Sure," cried the tenant men, "but it's our land. We measured it and broke it up. We were born on it, and we got killed on it, died on it. Even if it's no good, it's still ours. That's what makes it ours---being born on it, working it, dying on it. That makes ownership, not a paper with numbers on it."

The most important words in this quote, and Steinbeck's most forceful argument for what denotes ownership are as follows;

"That's what makes it ours---being born on it, working it, dying on it. That makes ownership, not a paper with numbers on it."