וּֽשְׂדֵ֛ה מִגְרַ֥שׁ עָרֵיהֶ֖ם לֹ֣א יִמָּכֵ֑ר כִּֽי־אֲחֻזַּ֥ת עוֹלָ֛ם ה֖וּא לָהֶֽם׃ (ס)
But the fields of the open land about their cities may not be sold; for that is their perpetual possession.
Read kabbalistic (mystical) interpretation of Leviticus 25:34: and classical mystical sources.