The Torah declares: "And if one strikes his father and his mother, he shall be put to death" (Exodus 21:15). The Mekhilta explains why this verse is necessary when the Torah already has a general law about assault. (Leviticus 24:20) states the principle of "an eye for an eye," meaning that a person who injures another pays monetary compensation proportional to the injury. Under that general rule, striking a parent would carry the same penalty as striking any other person: financial compensation for the damage inflicted.
But the Torah does not treat violence against parents as an ordinary assault. Scripture "took it out of its category," removing the case of striking a parent from the general framework of injury law and placing it in a more severe category. Instead of monetary compensation, the penalty is death.
This is the Mekhilta's explanation for why the verse exists. Without (Exodus 21:15), a person who struck his parent would be treated like any other assailant. He would pay damages and walk away. The Torah creates a specific exception for parental assault, elevating it from a civil matter to a capital crime. The same physical act, striking another person, carries radically different consequences depending on whether the victim is a stranger or a parent.
The severity of this law reflects the Torah's view of parental honor as a foundational principle of human civilization. The Fifth Commandment requires honoring one's father and mother. Striking them is not merely a violation of their physical person. It is an assault on the very structure of authority, respect, and gratitude that holds society together. The Torah treats it accordingly, with the most extreme penalty available under law.