Charles Ellicott Commentary Exodus 21:18-19

"And if men contend, and one smite the other with a stone, or with his fist, and he die not, but keep his bed; if he rise again, and walk abroad upon his staff, then shall he that smote him be quit: only he shall pay for the loss of his time, and shall cause him to be thoroughly healed." — Exodus 21:18-19 (ASV)

Severe assault that endangers life, but does not actually take it, is classified with homicide, as it approaches homicide, but is not to be punished in the same way. If death results in such a case, the crime is, of course, murder or manslaughter, according to the accompanying circumstances; but if death does not result, it is aggravated assault only. In such cases, punishment could not be inflicted by retaliation—the usual penalty under the Mosaic Law (Exodus 21:24–25)—without a risk of killing the person, which would have been an excessive punishment. The law therefore imposed a fine, which was to be set at an amount that would both compensate the sufferer for the loss of his time (Exodus 21:19) and cover the cost of his cure.