It means that all the land and countries in the earth belong to all people and are the property of any one person or group to decide whether to sell it to another person. It is like trying to sell air to someone, it doesn’t make any sense.
This quote makes emphasis on the fact that every land on Earth is a product of nature, and therefore, they inherently belong to all the people; these elements cannot be possessed or exchanged for monetary currency by anyone.
This quote is a form of protest, and its speaker stands for the free use of the elements of the Earth (land, air, water) without worrying about ownership issues.
