The water did not become two walls of water – that is impossible and poetic. Verse 21 says, a strong east wind blew all night and so created an artificial tide. When the Egyptian chariots tried too follow, they literally got bagged down. I have seen Tutankhamun’s chariot in Egypt. It is very light – and its wheels thinner than the side of my hand. Then the water flowed steadily back. Completely understandable if you live in East Anglia. When the tide turns in the Wash, it comes in faster than a galloping horse.
What was the Israelites’ response? They feared God and believed that he was really on their side.