If any party has sinned and is adjudged for death and is put to death, and you string up the body on a tree, you must not let the corpse remain on the tree, but must bury it the same day. For a strung-up body is a curse to God and you shall not spiritually block the land that your G-d is giving you to possess.
Why does the verse specify that not burying a body would block the specific land of Israel? Why does the choice of land actually matter?
Consider that in the Torah there is only one example of a person who is strung up on a tree: Pharaoh’s Baker, whom Joseph met in prison.
In three days Pharaoh will elevate your head and string you up on a tree; and the birds will pick off your flesh.”
This neatly summarizes much of the explanation of this verse: Egypt was a land fixated on death, where the existence of the living was centered around the preparation for death. Egypt was a land where bodies were strung up, and left there so the birds could eat the rotting flesh. Egypt is a land that cannot be elevated, that is perpetually spiritually blocked because of the way in which the living and the dead are treated.
But the Land of Israel is the land of connection and elevation: man to G-d, earth to heaven. Holy relationships are at the core of the mission of the Jewish people, as told to us in the Torah. Torah Judaism is all about doing what we can while we are alive. The dead cannot praise G-d.
We live for this world. And when we die, our bodies and souls are meant to return to their sources. Most critically: returning the body to the earth elevates it! In the Land of Israel, the land of the closest connection to the divine, it is essential that every person, through life as well as in death, has every opportunity to connect with G-d.
[Note that this is part of a series explicating a single verse: Deuteronomy 21:23. All work was done in collaboration with @susanquinn, @kidcoder, @blessedblackmith and @eliyahumasinter. The full series can be found on creativejudaism.org]