Rabbi Shimon HaTemani declared that God split the Red Sea in the merit of a single commandment: circumcision. The covenant of Abraham, inscribed in the flesh of every Jewish male, was powerful enough to part the waters.
The proof text is stunning in its scope. Jeremiah declares: "If not for My covenant, day and night, I would not have made the statutes of heaven and earth" (Jeremiah 33:25). God is saying that the very laws governing the universe — the orbits of planets, the cycle of seasons, the rising and setting of the sun — exist only because of a specific covenant. Without that covenant, heaven and earth themselves would have no reason to continue operating.
Rabbi Shimon then asks: which covenant operates both day and night? The answer is circumcision. Unlike other commandments that apply only at certain times — Shabbat (the Sabbath) comes once a week, festivals come once a year, tefillin (leather phylacteries worn during prayer) are worn only during the day — circumcision is present on the body at every moment, day and night, waking and sleeping. It never ceases. It is the one covenant that is permanently, physically active.
If circumcision is the covenant that sustains heaven and earth, then it is certainly powerful enough to split a sea. The Israelites who stood at the water's edge carried in their bodies the sign of Abraham's covenant — the mark that, according to Rabbi Shimon, holds the entire cosmos together. The sea had no choice but to part. It was obeying the same covenant that keeps the stars in their courses.