"And heal shall he heal" — the Torah doubles the word "heal," and the Mekhilta mines this repetition for legal content. If the victim was healed once but then relapsed, and was healed again, and relapsed again — even four or five times — the striker is liable to keep paying for treatment each time.
The doubling of "heal" establishes that the obligation is ongoing, not one-time. You do not pay for one round of medical treatment and walk away. As long as the wound keeps causing problems, you keep paying for the cure.
But the Mekhilta adds a crucial limitation. If new growths or complications sprouted because of the wound — around the wound site — the striker is liable. If complications arose that are not connected to the wound, the striker is not liable. The key phrase is "because of the wound." Causation matters.
The Mekhilta then draws a parallel between sheveth and ripui to establish this principle. "Just as sheveth is because of the wound, so ripui is because of the wound." Both categories of compensation share the same causal requirement. The striker pays only for consequences that trace back to his blow. Unrelated illnesses that happen to coincide with the recovery period are the victim's own responsibility. This causation requirement prevented the system from becoming an unlimited insurance policy, while still ensuring that the actual consequences of violence were fully compensated.