(Exodus 21:18) introduces the laws of personal injury: "And if men quarrel." The Mekhilta asks why this section exists at all. The Torah already states in (Exodus 21:24) the principle of "an eye for an eye." Why add a separate passage about quarreling men?
The answer is that "eye for an eye" addresses only the injury itself — the physical damage. It says nothing about two additional categories of compensation: sheveth (payment for lost work during recovery) and ripui (payment for medical expenses). These are not mentioned in the "eye for an eye" verse.
The quarreling-men passage fills this gap. (Exodus 21:19) says: "If he arise and walk outside upon his staff, then the striker shall be absolved; but his sheveth shall he give, and heal shall he heal." This verse introduces the obligation to pay for the victim's inability to work and for his medical treatment — two forms of compensation that go beyond the injury itself.
The Mekhilta's reading reveals that the Torah's system of personal injury law is far more comprehensive than "eye for an eye" alone. That famous phrase establishes the principle of proportional compensation for the injury. The quarreling passage adds the practical dimensions: lost income and medical bills. Together, they create a multi-layered system of damages that anticipates the full economic impact of violence, not just the physical wound.