With the countless recitations of the story of the "crossing of the sea" many details have been lost and others added, but its significance has remained obvious to the spiritual descendants of the Israelites -- Yahweh, with "a mighty hand" delivered Israel from slavery to freedom.
The Israelites are permitted to cross the sea on dry land, but the Egyptians are swallowed up and drowned in the returning water -- and thus did the Israelites escape the clutches of the Egyptian army.
In this panel, the sea is barely visible on the left, but has clearly retreated from its usual place, since no vegetation can be seen except at the feet of Moses, who apparently stands at the normal high water mark of the sea. The Egyptian army marches along the shore rendered by the artist as harmless stick-like figures (very small figures to the left of Moses’ staff). Moses, Yahweh’s emissary, stands protectively between the Israelites, safely tucked away somewhere on this side of him, and the object of their fear.
In the panel above Moses' head we see the river Jordan, the scene of another miraculous crossing told in the book of Joshua.