The Mekhilta records a sharp legal debate about how to determine the correct form of execution for a kidnapper. The Torah says a kidnapper must be put to death, using the phrase "moth yumoth" ("he shall surely die"), but it does not specify the method. So the rabbis looked for the same phrase elsewhere in Scripture to establish a precedent.
One sage compared the kidnapper to an adulterer, since both crimes use the phrase "moth yumoth." But another rabbi pushed back: why not compare the kidnapper to a blasphemer instead? The blasphemer's death sentence also uses "moth yumoth," and the blasphemer dies by stoning. If the same phrase governs both cases, then the kidnapper should also die by stoning.
This method of legal reasoning, called gezerah shavah, was one of the most powerful tools in the rabbinic arsenal. When the Torah uses the same phrase in two different contexts, the rabbis could transfer legal details from one context to the other. The logic is elegant: if God chose identical language, He intended identical treatment. The specific comparison matters enormously, since choosing the adulterer as the comparison case might yield a different method of execution than choosing the blasphemer. The debate in the Mekhilta is really a debate about which analogy is more apt, and the stakes could not be higher. The method of a person's death hangs on which verse the rabbis decide is the closer parallel.