Question: "Why is there a curse associated with hanging on a tree?"
Answer: Deuteronomy 21:22–23 teaches that there was a divine curse placed on a hanged person: “And if a man has committed a crime punishable by death and he is put to death, and you hang him on a tree, his body shall not remain all night on the tree, but you shall bury him the same day, for a hanged man is cursed by God. You shall not defile your land that the LORD your God is giving you for an inheritance” (ESV).
For most capital offenses covered by Jewish Law, stoning was the form of punishment. On some occasions the dead body would be hung in public as a deterrent to further crime. This law made it illegal to do so overnight (Leviticus 18:24–27; Numbers 35:3–34).
The apostle Paul referred to this law in relationship to Jesus and His death on the cross. In Galatians 3:13 we read, “Christ redeemed us from the curse of the law by becoming a curse for us—for it is written, ‘Cursed is everyone who is hanged on a tree’” (ESV). Jesus was cursed for us, hanging on the cross as a substitute for our sins. The law in the Mosaic economy was a foreshadowing of the redemption of man.
Another interesting detail is that the cross of Christ was sometimes referred to in Jewish contexts as a “tree.” Acts 5:30 states, “The God of our fathers raised Jesus, whom you killed by hanging him on a tree” (ESV). Acts 10:39 says, “They put him to death by hanging him on a tree” (ESV). See also Acts 13:29.
The concept of cursing and blessing in association with a tree is found in the larger narrative of Scripture. In Genesis 3 Eve and then Adam eat fruit from a tree from which they were forbidden to eat. In Revelation 22:14 the eternal state includes those who eat from the tree of life. A tree was involved in the entry of sin into humanity (through the tree in the Garden), the answer to sin for humanity (through the cross), and the ultimate removal of sin in eternity (through the tree of life).
Under the Mosaic Law, those who were hanged on a tree were cursed. The law made it illegal to leave the body hanging overnight. This law applied to Jesus, who was executed on a tree, although He had done no wrong. Jesus’ dead body was removed from the cross on the same day of His death and was buried. Jesus took the curse of sin upon Himself to redeem us from sin.