It marks the point in the Exodus at which the Israelites leave Egypt and enter into their wilderness wanderings. The Israelites at first were slaves to the Egyptians and later on Moses was selected to deliver them out of slavery. The Egyptians had to suffer ten plagues before the Pharaoh freed the Israelites. After which comes the crossing of the Red Sea. Moses held out his staff and the Red sea was separated into two halves by Yahweh and the Israelites walked on dry ground and crossed the sea. Behind them came the Egyptian army and Moses moved his staff and the sea became normal and with that drowned the whole of the Egyptian army.
Yahweh chooses Moses to lead the children of Israel out of slavery in Egypt and into the land of Canaan, which Yahweh has promised to them. The Egyptian pharaoh agrees to their departure, and they travel from Ramesses to Succoth and then to Etham on the edge of the desert, led by a pillar of cloud by day and a pillar of fire by night. There Yahweh tells Moses to turn back and camp by the sea at Pi-hahiroth, between Migdoland the sea, directly opposite Baal-zephon.
But Yahweh causes the pharaoh to pursue the Israelites with chariots, and he overtakes them at Pi-hahiroth. When the Israelites see the Egyptian army they are afraid, but the pillar of fire and the cloud separates the Israelites and the Egyptians. At Yahweh’s command Moses holds his staff out over the water, and throughout the night a strong east wind divides the sea, and the Israelites pass through with a wall of water on either side. The Egyptians pursue, but at daybreak Yahweh clogs their chariot-wheels and throws them into a panic, and with the return of the water the pharaoh and his entire army are destroyed (see Psalm 136:15). When the Israelites see the power of Yahweh they put their faith in Yahweh and in Moses, and sing a song of praise to the Lord for the crossing of the sea and the destruction of their enemies. (This song, at Exodus 15, is called the Song of the Sea).
The narrative contains at least three and possibly four layers. In the first layer (the oldest), Yahweh blows the sea back with a strong east wind, allowing the Israelites to cross on dry land; in the second, Moses stretches out his hand and the waters part in two walls; in the third, Yahweh clogs the chariot wheels of the Egyptians and they flee (in this version the Egyptians do not even enter the water); and in the fourth, the Song of the Sea, Yahweh casts the Egyptians into “tehomat”, the mythical abyss.