"And its owner, too, shall die" — the Torah pronounces a death sentence on the owner of a mued ox that kills a person. But the Mekhilta specifies: this death is "at the hands of Heaven," not at the hands of a human court.
The distinction is critical. Death at the hands of man means judicial execution — a court pronounces sentence and carries it out. Death at the hands of Heaven means God Himself enacts the punishment through providential means, without human intervention. The owner faces divine retribution, not earthly prosecution.
How does the Mekhilta prove this? From (Numbers 35:31): "You shall not take kofer for the soul of a murderer, who is liable to death." This verse establishes that those who are put to death by human courts cannot ransom themselves — no monetary payment can substitute for their execution. But the ox owner does pay kofer. The very existence of the kofer option proves he is not facing a human death sentence. Only those liable to death at the hands of Heaven can redeem themselves through payment.
The Mekhilta has drawn a bright line between two categories of lethal liability. Deliberate murderers face human execution with no possibility of ransom. Negligent ox owners face divine punishment with the option of monetary redemption. The Torah treats negligent homicide as less severe than intentional murder — severe enough to warrant a divine death sentence, but redeemable through kofer.