The precise reason why the burning of the bones of the deceased was considered a great crime in the ancient Near East is unclear, but it may have been connected with beliefs about resurrection from the dead. It was certainly seen to remove all honour and respect from the body of the deceased.1
1 Thus says the LORD: “For three transgressions of Moab, and for four, I will not revoke the punishment, because he burned to lime the bones of the king of Edom.