NOTES for Exo 14:1-31
The Hebrews' departure from Egypt is a true miracle, a miracle completely unexpected for the Egyptians. The point is that Moses immediately led the people in a direction completely different from where everyone thought he would go: not to Beersheba, where there was an old Yahwist sanctuary and where sacrifices could be offered to Yahweh and Passover could be celebrated. Instead of leading the people east and then north along the coastal road, he turns southeast toward the border, to the place where the Suez Canal is now, and where at that time there was a whole chain of lagoons connected partly with the Mediterranean and partly with the Red Sea. This chain of lagoons was called the Reed Sea, the very sea whose crossing the Book of Exodus describes (in the Synodal translation the Reed Sea is called the Red Sea). It is there, to the Reed Sea, that Moses leads his people.
The Egyptians understood that something unplanned had happened, the very thing they feared: the people had moved not where they had been permitted to go, but toward the border, clearly moving in order to leave the country. During the Exodus, Beersheba was on Egyptian territory, but Sinai never was, at least not in antiquity. No wonder the Egyptian border guard, made up of light chariots and cavalry, immediately set out after the Hebrews to keep them from leaving and blocked the fugitives in the area of the Bitter Lakes, where the Reed Sea was at its narrowest.
When, at what moment, does Moses decide to leave the country? It is hard to say exactly. It is possible that he already knew this when he called the people to celebrate Passover. More than that, however, he still did not know exactly by what route he would lead the people out of Egypt. Here he simply had to follow God, and Moses understands this even when the situation appeared completely hopeless, when the Egyptians had blocked the people in the area of the Bitter Lakes.
That is when the miracle happened, the one neither the Hebrews nor the Egyptians expected: a strong wind blew the water out of the Bitter Lakes, temporarily exposing the bottom, which was a sticky salty muck. Walking through that muck was not easy, but neither chariots nor riders could move through it faster than a person on foot. An effective pursuit did not work out; the gap between the departing Hebrews and the Egyptians pursuing them inevitably had to remain until they reached firm ground. The Hebrews stepped onto it first, and then the wind died down. The water rushed back to its usual place, covering the Egyptians who had been pursuing the Hebrews. Egypt was behind them, and ahead lay freedom and the desert.