One of the SD’s favorite books as a kid was the Good Earth by Pearl S. Buck. The book is about a poor farmer in China who amasses tremendous amounts of land. At the end of the book when he is an old man, his rich sons do not want to work the field and want to sell. He freaks out. Never sell and the book ends.
Daf 20-21 has a mishna that says we cannot sell land in Israel to idol worshipers. The Mishna also says we cannot sell land in Syria to idol worshipers. The Talmud tells us that by selling land, we are removing from the the obligation of giving Maaser.
The SD now understands the old farmer in the book. He did not need the land anymore. His kids had all the money. The talmud’s reason for not selling is great. We might not need the land, but others need us to keep the land. Others depend on us. Others depend on the land. Giving Maaser is metaphor for giving and sharing. The ownership of land triggers the need to give and to share.