A gentile once confronted Rabbi Yohanan ben Zakkai with a cutting observation: "Your ceremony of the red heifer looks exactly like witchcraft. You take a cow, burn it, grind it up, mix the ashes with water, sprinkle it on a person who touched a dead body, and declare him clean. This is sorcery."
Rabbi Yohanan did not flinch. "Tell me," he replied, "what do your own people do when someone is possessed by a demon?"
"We take certain herbs," the gentile admitted, "make a fumigation, and the demon departs."
"Then let your own ears hear what your mouth has spoken," Rabbi Yohanan said. "If herbs and smoke can drive out a spirit through natural means, how much more effective are the sacred ashes of the heifer — which carry divine authority — for driving away the spirit of impurity?"
The gentile left, apparently satisfied. But Rabbi Yohanan's students were not. "Master," they said, "you brushed him off with a straw. What is the real answer?"
Rabbi Yohanan looked at them gravely. "By your lives," he said. "The dead body does not actually make a person impure, and the water does not actually make him pure. Rather, it is a decree from the Holy One, blessed be He. God said: 'I have set down a statute. I have issued a decree. You are not permitted to transgress My decree.'" The Pesikta (40a) and the Midrash Hagadol record this as the definitive teaching on the red heifer — the ultimate commandment that defies human logic and demands pure obedience.