The Torah's treatment of adultery presents a puzzle that the Mekhilta refuses to ignore. In one verse, the commandment thunders from Sinai: "You shall not commit adultery." In another, (Leviticus 20:10) spells out the consequence: "The adulterer and the adulteress shall be put to death." If the Torah already prescribes the death penalty, why bother stating the prohibition separately?
The Mekhilta's answer reveals a fundamental principle of how Torah law operates. A punishment alone is not enough. Without an explicit prohibition — what the rabbis call an azharah, an exhortation or warning — a court cannot impose the penalty. The death sentence in Leviticus tells us the consequence, but only the commandment at Sinai provides the formal legal warning that makes enforcement possible.
This distinction runs throughout rabbinic law. God never punishes without first warning. Every penalty in the Torah is paired with a corresponding prohibition, and if a prohibition cannot be identified, the punishment cannot be carried out. The Mekhilta is teaching that divine justice is never arbitrary. It operates on a principle of fairness that would be recognizable in any legal system: you cannot punish someone for breaking a rule they were never told existed.
The doubling that seems redundant is actually the architecture of mercy built into the system. Israel received the warning at Sinai before any penalty could ever be applied. God, in effect, gave everyone fair notice. The seventh commandment is not just a moral statement — it is a legal prerequisite, the exhortation without which the entire enforcement mechanism would collapse.